What happened to Dave Sim — more than once — while writing Cerebus the Aardvark. With increasing frequency, he would halt the plot in order to lecture at length about his new religion/theory-of-everything that he created from equal parts Old Testament, conspiracy theory and vast galloping misogyny. Any characters or plot points that didn't fit his new view on life were hammered flat until they did. Note that this is unrelated to Cerebus Syndrome, which occurred to the comic long before his breakdown.
Dave Sim redefined the comic book industry in two ways: First, by showing that it was possible for a single independent creator to make and publish their own work and be hugely successful. Second, by showing why this can be a really bad idea in the long run. Having a schizophrenic break without any editors, managers, stockholders, or anything else to rein you in has a pretty terrible impact on your ongoing storyline.
Dave Sim's collaborator Gerhard also suffered this due to it getting more and more stressful to work on Cerebusnote due both to increasingly-tight deadlines and him no longer enjoying Sim's writing and to work with Sim. While his breakdown didn't affect the comic itself, it greatly affected his output afterward; once he left Aardvark Vanaheim, he couldn't bring himself to do any drawing for almost six years. Since then, he's dabbled in illustrating children's books and seems to have more-or-less recovered (although a cryptic line on his website mentions that some of the proceeds from his sales go towards his therapy bills).
Grant Morrison made a point of feeding his own personal life and interests into The Invisibles, including making a deformed villain based on the miscarriage that his girlfriend had. Weirdly, this also went the other way; Morrison is a magician and believed that in The Invisibles he was creating a giant magical work that would reshape his life. Whether or not this is the case, there were some odd moments of synchronicity — like the time his author insert character, King Mob, was shot in the chest, and Morrison was subsequently hospitalised with a collapsed lung.
Morrison is somewhat of a master of this trope, as he wrote about the death of his cat being used in his ground-breaking Animal Man series. In issue 26, he notes how as a creator he simultaneously feels the pain and relishes the opportunity to craft this into a story.
Morrison subsequently deliberately wallowed in negativity (resulting in at least one suicide attempt) in order to write the very dark comedy The Filth. Morrison saw it as a way of passing through the Kabbalistic abyss that represents the darkness at the depths of the human heart and mind, but he's like that.
Morrison also admitted that personal tragedies contributed to the very dark "Planet X" arc of New X-Men.
All-Star Superman was largely Morrison's way of dealing with his father's death. That theme also ran into Seven Soldiers and his Batman run. When it was pointed out that he didn't really touch on motherhood as much Morrison acknowledged that it might have largely to do with the fact that his mother is alive and perfectly healthy for the foreseeable future.
James O'Barr created the comic The Crow to deal with his grief over losing his fiancée Bethany, who was killed by a drunk driver.
Steve Ditko is the revered co-creator of the Marvel Universe among other creations. However, when he does not have a collaborator like Stan Lee to restrain him (or add his more humanistic viewpoint), his later stories tend to be barely more than self-righteous lectures about Objectivism.
When Peter David started writing The Incredible Hulk, he promised that he wouldn't kill off Betty Ross, Hulk's long-time love interest, partly because the character was one of his wife's favorites. Years later, he and his wife went through a painful divorce. Not long after that, Betty Ross met a rather painful end in the comics. David has since come out and admitted that the strip was more than a little influenced by his real-life circumstances and, had things happened differently (not limited to the fact that he was soon taken off the book), he would have let Betty live.
Geoff Johns' sister died in the crash of TWA Flight 800. Surprisingly, nothing horrible happened to the character based on her, the Star-Spangled Kid (now known as Stargirl). However, the situation did inspire an influential arc of JSA, in which Atom Smasher loses his mother in an airplane crash, then substitutes the villain Extant — who killed Al's godfather — in place of his mother after a big reality-altering plot implodes. This led to the revitalization of Black Adam and the series' arguable high point, Black Reign.
We eventually introduced a character named Mystek, but I killed her off when her miniseries was not approved. Mystek was supposed to be a creator-owned character, developed under a first-look deal, and I was instructed to put her into JLTF to introduce her to the fans in preparation for her miniseries. Then there was no series, so I shoved her out an airlock in JLTF #32.
Adventures of Barry Ween creator Judd Winick wrote a touching graphic novel about his friendship with fellow MTV's Real World co-star Pedro Zamora and Pedro's eventual death, Pedro And Me. Since then, much of Winick's work - particular at DC Comics - has consisted of Very Special Issues involving HIV and homosexuality.
Winick also married his MTV's Real World co-star Pam Ling in 2001. Since then, he has also made an effort to introduce more minority characters in his comics and to utilize underrated minority heroes, particularly Asian females (such as Grace Choi). While this would normally be commendable, Winick's attempts at increasing diversity have been almost universally ham-fisted, with one of the most grievous examples being Green Lantern #150, in which Kyle Rayner learns that his long-lost father is a Mexican immigrant... despite his father having an established history as being a deep-cover government agent who worked in Ireland and Kyle having already met his very-Caucasian uncle.
Jack Chick went through a Creator Breakdown that, for all intents and purposes, is still going on. He suffered a stroke in '96, and his ability to draw has slowly deteriorated ever since.
Rob Schrab's difficult breakup and struggles with legal ownership of his characters as well as difficulties in getting his work adapted into other media combined to completely derail Scud The Disposable Assassin towards the end of its initial run; the series starts out as a slightly surreal action comedy, but gets completely derailed near the end and concludes rather abruptly with the protagonist's girlfriend butchered by sadistic angels, and a general theme of "there is no God." The 2008 series reboot is much less bitter and has a much more satisfying ending.
After the death of Jeph Loeb's son, Sam, there was a notable change in the theme and mood of Loeb's comics writing. He used one of his scripts and created "Sam story" comics for Superman/Batman, and then retired from comics. Later his friends at Marvel convinced Loeb to return to the industry and work for Marvel. Since then Loeb wrote a mini-series about how several characters mourn Sam's death through the proxy that is Captain America, dropped a steaming load of controversial plot onto the Incredible Hulk series, and tore through the Ultimate universe with Tomino-like reckless abandon. Losing a son is never easy...
He also gave the new Nova the name Sam Alexander in honor of his son.
Hergé wrote Tintin Tintin In Tibet largely as a sort of therapy, to resolve the emotional issues he had following his divorce and the distressing dreams he'd been having that involved vast white landscapes. It is widely considered to be his masterpiece.
However, it caused Hergé to undergo another Creator Breakdown — after the book was released, he decided that there was no way he would ever write such a good Tintin story again, and effectively gave up trying to do so. The remaining three Tintin stories were released at a far slower rate than the previous ones, and took the form of experimental character pieces which tended to mock the characters Hergé had been writing over the previous decades. Tintin and Alph-Art might have seen a return to the more traditional storyline, but we'll never know since Hergé sadly suffered Author Existence Failure with the story only half-finished.
There's also a shot at relative newcomer Batwing getting his own title while several of Robinson's characters were slated to be sent to Comic Book Limbo or retconed out of existence.
Everything Ivan Brunetti has ever written. It's a wonder that he's still alive and drawing.
Jack Kirby had this bad in the late 1960s. Oh sure, he was the King of Comics, and his SilverAge Marvel stuff is considered some of the best comics ever, but he had a lot of personal issues on his plate. He was getting more and more flustered over his lack of creative control, he couldn't negotiate for a higher salary or even make sure that his family would be provided for if anything happened to him (nowadays this stuff is guaranteed in the industry), Stan Lee was getting all the good press, and he was terrified that he would lose his job if anybody found out that he was going blind in one of his eyes. Then came the 1969 Silver Surfer issue that lost him his crown.
Kirby was angry that Stan Lee got credit for the Surfer when the character was his own independent creation. He was angry when Lee began writing a Silver Surfer series and got somebody else to draw it. He was angry that Lee concocted an origin story for the Surfer that was completely different from his own idea. And then Lee asked Kirby to draw a fill-in issue for the book, and mentioned that this issue would change the Surfer from a philosophical pacifist to a berserk enemy of all mankind to help boost sales. Kirby gave Lee exactly what he asked for. The highlight of the issue is supposed to be an epic battle between the Surfer and Black Bolt, but the Surfer gets pissed halfway through and just leaves. The penultimate page is uncharacteristically dark, especially for Kirby, as the Surfer sits and lets his rage take him over completely. The final page is a full-sized portrait of the Surfer's tormented face screaming in fury and declaring that soon the universe will fear his wrath. That's right. Jack Kirby drew his own creator breakdown right into the Surfer's mouth, handed it over to his bosses, and jumped ship to DC Comics and other things. Beware the Nice Ones indeed.
Ironically Lee pushed Kirby into doing his last great burst of creativity for Marvel with that last Silver Surfer. Kirby was pretty much marking time on the Fantastic Four for his last twenty or so issues, deliberately keeping all his good ideas to himself so that he could do them over at DC without Lee.
Franquin experienced in fact various depressions throughout his career, the first one being on the 60s, while the "Dark Toughts" part of his work happened in the 70s. In the early 60s, Franquin's break down affected his work on the "Spirou et Fantasio" saga, resulting in the unusually dark "QRN sur Bretzelburg" album. The album deals with themes such as War Trade and totalitarian states.
Lewis Trondheim treats of this issue in his essay Désoeuvré (Loose End) and mentions many comics authors.
Peter Laird sold Teenage Mutant Ninja Turtles to Viacom because he was distancing himself from his loved ones. Go read his blog to hear more.
Dwayne McDuffie's final JLA arc was basically a metaphor for his then-deteriorating relationship with DC Comics. Near the end of the story, most of the League's members have quit (in real life most were taken away from Dwayne due to Executive Meddling) and several other members, notably Black Canary, begin to question their commitment to the team and whether or not they even care enough to continue protecting the world.
In later interviews for his Justice League: Crisis on Two Earths movie, Dwayne would slyly mention that it was refreshing to get to write a Justice League story without having other people mucking up his work.
An interesting if entirely fictional variant came in the Superman one-shot 'Under A Yellow Sun'. After years of mentioning Post Crisis Clark Kent's career as a novelist, we actually see some, featuring a swashbuckling hero through whom Clark works out his other career's ups and downs. During a particularly bad patch in which his Sisyphean battle with the Corrupt Corporate Executive version of Lex Luthor is going not well at all, he has his character finally kill the bad guy, a choice for which Lois lambastes him. After reminding himself of some necessary truths about the never-ending-battle, he has the character do what he has always done, sparing and even saving the life of the worst person he knows. The irony comes when he receives praise for the novel from closet page-turner popcorn-reader Luthor.
Jamal Peppers, artist for the first four parts of Sonic The Hedgehog Mega Man Worlds Collide suffered a more literal one when he had to be hospitalized before he could finish the fourth issue. Another artist jumped in to finish it up.
In-universe in Scott McCloud's comic Uninformed Bob, which depicts a gag-a-day comic strip written by a cartoonist who slowly goes insane.
In-universe in Knights of the Dinner Table: Jolly Blackburn wrote a "review" of the Gary Jackson Hack Master novel The Lady is a Thief. The protagonist was based on Gary's wife Heidi, and becomes evil and vicious for no good reason at the point of the novel that was written during Gary's divorce. According to the review, the book was pulled from publication after Heidi sued for defamation, and only a few stray copies remain in circulation.