I didn't usually have these experiences when taking melatonin until recently when I tried a new brand that has been lying around for a while. With this brand it's almost everytime I use it even in extremely low amounts (below 200mcg) that I have these reactions but practically only when I wake up and not the night before when I actually take it.
I will tend to wake up with real paranoia or very strong emotions as seen in borderline pd.
Several of my emotions are greatly enhanced and my perception is altered to the point of feeling hurt by everyone and extreme hatred. Not only this but the melatonin can also worsen sleep quality considerably which very strongly occurs together with the paranoia and emotional side-effects.
I suspect this has to do with the 5HT2A receptor, but doesn't everything?
I don't have any characteristic symptoms of borderline personality disorder and paranoia has never been an issue of mine.
It turns out that one of the recognized side-effects of melatonin is indeed paranoia. I just wanted to share my own experience, especially in relation to borderline personality disorder.