Assuming you're asking for world building thoughts, I've got a few. But they depend on three main things:
1) How aggressive are these monsters? Are we talking sit in the corner and howl, or rampage around a city killing people? Or maybe it varies by mental issue?
2) How powerful are these monsters? Let's say a kid transforms and is aggressive. Can the teacher restrain them, or is that a job for the police? Or is it beyond everyone and you just have to get away from them until they revert back?
3) How common is this? In a large (million plus) city, is this a daily event, a yearly one?
Without that information, my comments below are fairly general:
A) Cultures probably won't react all the same way unless you're going for a 'one world order' feel. Some cultures may react with constant surveillance then medication or imprisonment of those showing signs of potential issues. Others, as you say with more focus on therapy and mental health, but others would probably treat this as a religious issue, having evolved or developed their own treatments. And that's without getting into the question of how it's viewed in a society. Are they viewed as 'embarrassing, but not a big deal,' 'shamefully giving in to their own demons,' or 'asking for help they are owed,' or something else altogether?
B) Depending on the answers to 1 and 2 above, world history ought to be radically different. If traumatizing a bunch of people results in powerful rampaging monsters, then I'm not real sure how you successfully launch a military campaign, or engage in any sort of slave trading.
C) Regarding controlling the transformation or triggering it artificially, the value of that will depend on the answers above, but the general notion of this 'mental illness makes you a monster, or gives you superpowers,' may upset some folks. Not trying to dissuade you as it seems like an interesting idea, but you may want to run it past a sensitivity reader with experience in those issues, which definitely isn't me.
Edited by ECD on Dec 1st 2021 at 5:25:13 AM
Their actions largely depend on the person and what set them off. The law does indeed vary from place to place on whether or not, for example, a person is considered responsible for what they do while transformed. In at least parts of the United States, school faculty are issued tranquilizer darts as a precautionary measure, though that is fairly controversial. Power is variable based on multiple factors, and (involuntary)transformations usually become less common as a person matures and gains better control over their emotions. For example, babies statistically transform far and away the most often out of any age group, but remain fairly easy to deal with. People with PTSD will transform just about every time they experience it, and it’s fairly common for people who die abruptly to transform as it happens. Opinion on all this varies from extremely controlling and repressive cults/regimes/what have you to “it is what it is” to people who consider their alternate forms (which I now realize I don’t have a name for) their true selves.
Specifically that people overwhelmed by negative emotions transform into monsters that act as metaphors for their psychological issues. It’s temporary for the most part and generally just considered a fact of life, having been present for all of recorded history with archeological evidence suggesting it goes back even farther, but nobody knows why it happens. I feel like mental health would be discussed somewhat more openly than in reality, if only to mitigate the problems that transformations cause. It can be repressed to some extent, but that only goes so far. I’m thinking that there are a minority of people who have gained active control over their transformation by some means, but also that if there were an antagonist it would be a group with some means of triggering transformations in others artificially.