You've seen those common TV commercials about depression. "Are you less interested in things you used to enjoy? Maybe you're depressed. Depression hurts." Etcetera.
Everyone feels down sometimes (with the possible exception of The Eeyore, who's always feeling down). However, there are various types of clinical depression, which is a very common psychological problem. Up to 1 in 5 people will experience it at some point in their lives.
Antidepressants can help those who are clinically depressed, of course, although counselling tends to be very helpful as well. For minor to moderate depression, counselling is usually at least as effective as medication.
The major signs of depression, copied over from the Useful Notes page on suicide's overview of depression, are as follows:
Persistent feelings of sadness or worthlessness, for at least two weeks. (Obvious sign of depression.) A common description by sufferers is that they feel "empty" or "hollow" inside. Unfortunately with teens, it is often dismissed as typical moodiness. This leads to the perfect storm of feeding their self-destructive thoughts, making them reluctant to seek help from adults, and instilling the belief that they have to prove their unhappiness is genuine—regrettably, some of those attempts work.
Lack of interest in previously enjoyed activities for at least two weeks. (Obvious sign of depression.) An extreme sign is when the person is trying to enjoy themselves, but cannot even feel anxious about their lack of enthusiasm. They may simply stop participating in their hobbies, but some people retreat into their homes altogether and rarely leave the house.
Frequent breakdowns and crying episodes. (Known, but exaggerated.) This is rarely witnessed first-hand, despite common media depictions. Depressed people in real life will more often seek out quiet and isolated places during such episodes, either because they want privacy or because they want others to notice that they're gone. Whether male or female, the sufferer may have an (un)conscious desire to be found, as the act has a dual purpose of validating their feelings and giving them "proof" that someone cares about them.
Sleeping too much, or being unable to sleep. (Known, but may not be recognized as a symptom in itself.) This is frequently due to the chemical imbalances.
Unexplained, frequent aches or pains due to the immune system shutting down. (Little-known/overlooked.) A variant of this is when minor injuries or illnesses take too long to heal, such as a cold persisting for a month or scrapes and bruises lasting for days. Those with no medical experience often cannot connect this to depression.
Feeling cold in inappropriate weather, or the coldness persisting in adequate warmth. (Little-known/overlooked.) This may be the reason for the stereotypical depictions of a black-clad "emo" teen, as dark colors absorb and retain heat better than light clothes. It also is one of the most frequently-overlooked symptoms, as wearing sweaters is not unusual in certain climates and even the person in question may not realize that this is a symptom.
Changes in appetite and the subsequent weight gain/loss. (Little-known/overlooked.) As stated before, depression involves large-scale physiological changes, and subsequently affects the person's appetite. On the other hand, this can be hard to detect as those with decreased appetite will either remind or force themselves to eat normally, and those with increased appetite may hide the bulk of their overeating. Both sides may play it off as insignificant, or even joke about it to keep people from worrying.
Other signs include:
"Difficulty concentrating, remembering details, and making decisions" This is easy to over-look if the sufferer is also experiencing insomnia. It may also be difficult to distinguish between this symptom and ADD/ADHD.
"Irritability, restlessness." (Easily-Overlooked)
"Psychomotor agitation or retardation nearly every day."
"Headaches, cramps, or digestive problems that do not ease even with treatment."
While these are the seven major signs, it is not the case with everyone and there are many more symptoms that may be particular to a specific person.
Something else to note is that some of the most recent research on depression shows that the "serotonin imbalance" of common antidepressant advertising may only be one type of depression - some unmedicated depressives have absolutely normal serotonin levels, for example. Also note the overlap between chronic fatigue syndrome and depression, some pain syndromes and depression, and PTSD or complicated grief triggering depression. While the research isn't completely in yet, it does seem to point to at least four conditions that are under the umbrella of "unipolar depression": one where emotional symptoms are dominant and there are few physical symptoms, one where physical symptoms are more dominant and either a result of or even possibly causing the emotional symptoms (which is what CFS and similar syndromes appear to be), one where both physical and emotional symptoms exist, and one triggered by painful and traumatizing life experiences such as abuse or combat stress or the loss of a loved one and its attendant grief. The point being - every case of depression is, in a way, unique to the person suffering it, even if it falls generally under "depression" or these symptoms or these types.
That said, there are some very common misunderstandings of depression and related conditions, some of which are propagated by Hollywood, others of which are propagated by sometimes well-meaning people, the pharmaceutical industry, and many other sources in the mainstream.
"Depressed people must be sad all the time, if you're ever happy, you're not really depressed." This is one of the big ones (big enough that it's even led to lawsuits in a few cases, specifically related to insurance, workers compensation, and the like.) The reality of depression is that sufferers do have good days as well as bad, and maybe even good weeks or months as well as bad. Or good minutes or hours in the middle of bad days etc.
Some reasons why this is
Depression sufferers may feel incredibly bad but try to do things to make themselves feel temporarily better or to meet the expectations of others in their lives as well - this is actually often a cause of co-morbid addictions, in that sometimes, substance use will temporarily lift the depression enough to make being The Alcoholic, for example, at first seem a welcome relief. Psychological addictions are another way of coping; some sufferers may watch more television, read books, or find some other form of escapism as a way of relieving the stress of their situation.
Nicotine and opiate addictions are specific risks of depression - nicotine because it is a stimulant with some possible positive effects on brain function (at least in current users), and opiates because they do have an antidepressant effect, and especially in physical symptom predominant cases, may provide relief. If you are prone to depression you should use neither unless opiates are prescribed by your doctor with full knowledge of your condition and when all other options have been exhausted. If you're already a smoker, nicotine replacement/harm reduction (via using gum, lozenges, patches, or vaporizing devices) is something to consider, as it provides the possible positive effects without as many of the harmful ones that smoking or chewing tobacco provide.
As a side note on opiates, some research is showing at least one form of depression possibly exists where the depression is caused by lack of endogenous opioid production/failure of the body to respond to its own levels of endorphins (e.g. the endorphin system is screwed up) as opposed to lack of serotonin, in which case opiates could be a proper medication. That said, this is not a reason to abuse opiates for depression relief, because the only things that indicate this variant are either preexisting drive for/near-instant addiction to opiates and/or the failure of serotonin-related medication interventions. That said, if you do have the combination of opiate craving and failure of SSRI and SNRI type drugs (and especially if chronic pain/fatigue/anxiety are severe parts of the depression), trying suboxone or a low-dose time-released long-acting opiate, under a doctor's supervision, may well be a good idea.
Bipolar I's other side is mania, the polar opposite of depression. Mania is an illness in and of itself, and arguably one even more destructive than depression because it tends to lead to far more dangerous and/or irresponsible behavior at its extremes, which Bipolar I sufferers tend to have.
Bipolar II or cyclothymia alternate sometimes severe depressions with mildly manic (in Bipolar II) or normal and healthy (in cyclothymia). These periods of "relief" do not make the depressions any less "real" or any less disabling.
In a similar vein, there are types of depression that are dependent on triggers. These are generally associated with PTSD, complex PTSD, and complicated grief (though sometimes a trigger can switch a BPII or cyclothymia sufferer to a depressive cycle). Sufferers of these types of depression are often very likely to be dismissed, mocked, or considered to be lying because they often seem like mentally healthy people unless they are in a situation where the trigger is unavoidable. This may prove a major problem for those whose triggers involve things in traditional workplace or family situations - they can be considered "lazy" for not working certain types of jobs or inferior for not wanting a traditional family situation, and the scorn and disgust this earns destroys self-worth and can make the depression spread from the triggers to a far more generalized depressive condition.
For many depression sufferers, the depressions can go away (generally when being treated and/or not under stress) and come back (when treatment is ended or fails, or when a painful/stressful life event happens). Depression is generally a "relapsing-remitting" condition. Even during a depressive state, a sufferer's mood can lift for short periods of time only to sink again.
Finally, for some who have uteri, depression symptoms can be tied to the menstrual cycle or to pregnancy. Note the existence of PMDD and post-partum depression.
This can be a double problem for some FTM transgender people - being in the wrong body alone is depressing, and the hormonal fluctuations that serve both to cause chemical imbalances themselves and as a reminder of what is causing them. This can sometimes be almost a mental form of And I Must Scream - for those who've never experienced it, imagine being at the mercy of mood swings and cycles that can be uncontrollable and change on a biweekly to monthly basis... and which are predictable but unstoppable.
"Depression doesn't mean other mental illnesses or have much in common with them." This one's true to some degree and is a form of Positive Discrimination to limit stigmatization of depression sufferers, but there's many conditions that are co-morbid to depression. There are also other mental illnesses for which depression is a symptom (the physical illnesses for which it is will be addressed below). To use a physical comparison, much like pneumonia being both a condition itself as well as a possible symptom of other illnesses, so can depression.
Mental conditions co-morbid to depression
The big one is anxiety. Most anxiety sufferers will have some degree of depression, and quite a few depression sufferers will have some degree of anxiety disorder. The reason is simple: both seem to originate from imbalances of the same brain chemicals, as well as similar environmental triggers and such.
Addiction is often also co-morbid to depression, for the reason that self-medication (and sometimes doctor-approved medication for other conditions, the big ones being here painkillers or benzos) can immediately make a depressed person feel temporarily better or, in the case of bipolar I and II or cyclothymia or similar, put them into a better cycle. That doesn't necessarily mean such self-medication is bad (see later) but that it must be very carefully watched, as it can easily begin an addiction to the means of feeling better, as opposed to understanding the means as a temporary form of relief or a way of intentionally escaping a bad cycle.
Eating disorders can be co-morbid to depression because depression itself changes eating patterns, and an eating disorder may well result - especially if the depressed person wishes to lose weight and stops eating in order to do so or alternately, eats to feel better.
Self-injury is sometimes co-morbid to depression and is not generally a suicide attempt or being an Attention Whore or Emo Teen stereotype - it is a way to feel or release emotions.
Mental conditions for which depression is a symptom
Addiction as above, except that instead of the depression causing the addiction, the addictive behavior's "crash" or "low" phase leads to the depression. Very common in stimulant addicts (cocaine and amphetamine/methamphetamine users, and to a lesser degree, nicotine and caffeine users) and alcoholics.
ADD/ADHD, because of the lifestyle results of especially severe ADD/ADHD leading to stressful life events and a feeling of helplessness or powerlessness over what seems to be a disorganized and scattered life - as well as to the side effects of badly managed ADD/ADHD medication in some instances.
Autistic spectrum disorder, particularly among women, because so much mental resources gets put into trying to cope with impaired social skills (either by emulating others or trying to manage the consequences of not) that it exhausts mentally and leads to a feeling of alienation.
Anxiety, as above, except instead of the depression beginning the anxiety, the anxiety disorder was the primary illness and created the depression.
Bipolar I and II are unusual cases, in that they are depressive illnesses, but as opposed to major "unipolar" depression where the "bad" times are all lows, bipolar (formerly called manic-depression) is such lows interspersed with periods of another illness called mania, which is the "polar" opposite of depression. In Bipolar I, the manic periods are extreme and almost stereotypical, sometimes leading to psychosis (total loss of connection to reality and acting out on said delusions or hallucinations). In Bipolar II, the manic periods are mild to moderate and comparable to someone constantly while in the manic phase acting as if what a "normal" person would be like after a couple Adderall or a line of cocaine, in that they are not so manic as to be disconnected from reality entirely or hallucinating, but definitely "high" or "sped up."
Sufferers of various personality disorders can also suffer from depression, both as a co-morbid chemical imbalance, from how the disorder has caused them to be treated in life, or from the consequences of their behavior or their interpretations of themselves or others. Borderline, narcissistic, and histrionic can often be co-morbid to depression.
PTSD, complex PTSD, and complicated grief are often causes of depression and depression is often co-morbid to them. They are mental injuries as opposed to mental illnesses, in that they do not, themselves, arise from brain chemistry alone but from horrifically traumatizing life events (abuse, combat, disaster, violent assault, rape, the sudden loss of loved ones), but the pain and helplessness can easily begin a depression that takes on biochemical characteristics as it continues.
Schizophrenia in which depression can be a "negative" symptom ("positive symptoms" are the delusions and hallucinations that are more characteristic of the illness) and due to the stigmatization that the diagnosis itself provides.
"Depression is always the direct result of a chemical imbalance of serotonin in the brain." Again, this is true in some cases of depression, but it is also a commercial oversimplification of what can be a very complicated mental condition, a symptom of a physical condition where the imbalance is of something else entirely, or even the result of abuse. This is why anyone suffering from any form of depression needs a thorough physical and mental examination rather than a prescription of whatever antidepressant is advertising the most - especially because some of the physical causes can be fatal if left untreated in the pursuit of "it's all in your head."
Physical conditions for which depression is a symptom
Abuse can definitely lead to depression, for obvious reasons. If someone is living in an abusive situation, it almost always has an emotional component and therefore emotional effects.
Addison's disease can have exhaustion and depression as a symptom. Sometimes with no known cause, other times due to a tumor on the kidneys or pineal gland, it can be fatal if not diagnosed and treated properly.
Anemia is often mistaken for depression. Someone who is anemic is not getting enough oxygen via their bloodstream to their body and brain - the body is in effect dying from blood loss and oxygen starvation, which leads to depression symptoms among others. A complete blood count is essential.
Any number of organic brain illnesses or injuries, too many to list individually, but anything from ALS to multiple sclerosis to traumatic brain injury.
Cancer can cause anemia or hormonal imbalances that lead to depression, or even directly affect the functioning of the brain, depending on the location of the tumor (a tumor causing bleeding in the GI tract or uterus leading to anemia, a thyroid cancer leading to hyperthyroidism - see below for its own entry, or a brain tumor causing brain functioning changes.) Diagnosed cancers can also lead to depression from the stress of the diagnosis and life with it, and some forms of chemotherapy can be physically and mentally exhausting.
Chronic pain can lead to depression or depression-related symptoms - treating the pain or the cause of pain properly will help.
Chronic fatigue syndrome can be a cause of depression and can manifest in ways that are easily mistaken for depression - just look at the crossover symptoms between CFS and depression.
Epilepsy can cause symptoms similar to depression, ADD/ADHD, or even psychotic conditions in some temporal lobe cases. Seizures can appear as depressive or manic or hallucinatory episodes, and post-seizure fatigue can seem to be depression.
Influenza can be a cause of a short-lasting form of depression for up to two weeks while recovering from some types. This is short-term and will generally go away with rest and self-treatment. If you've just had the flu and feel depression symptoms, it's better for you both financially and mentally to rest and self-treat as needed unless it lasts longer than two or three weeks.
Insomnia can lead to depression and anxiety, as well as be a symptom of it.
Hypothyroid almost always causes depression-like symptoms, and hyperthyroid can cause depression and/or symptoms similar to bipolar. Both can be fatal if unrecognized and untreated both from the depressive symptoms possibly leading to suicide, and to an unrousable coma in hypothyroid patients or thyroid storm and a heart attack in hyperthyroid.
"Treatment consists only of antidepressants and neuroleptics." There are many other options to treat mild to severe depression, and while antidepressants and neuroleptics are one option, they are not the only legitimate option that is used.
Adaptations and treatments aside from/along with traditional medication
Talk therapy is the biggest one and most important. In fact, some studies have shown talk therapy (especially of the cognitive-behavioral model, but any will do) to be as if not more effective than medication in prolonged remission of depression. If you are moderately to severely depressed, you need to be doing talk therapy along with your medication with an understanding counsellor with whom you have a good rapport. If you are mildly to moderately depressed, doing talk therapy alone without medication may be most advisable because it has no side effects and will not, generally, make matters worse before they get better.
Lifestyle changes are another option to be used in conjunction with talk therapy and/or medication. These can range from leaving an abusive situation or triggering situation or changing one's beliefs or expectations to simpler things such as getting enough rest and exercise, proper nutrition, getting a pet, or developing more satisfying friendships and relationships. One purpose of talk therapy is to guide you in helping make any of these that you may need to make.
Alternative medications are possible in cases involving hormonal causes - thyroid hormones or sex hormones. Another alternative form of medication is the prescribed and monitored use of cannabis, psilocybin, MDMA, or even opiates - very experimental at the time and illegal outside of official studies or prescriptions, but some results have been reported in depressions that have been otherwise resistant to traditional antidepressants.