I'm looking at the wikipedia article on Melatonin and noticed that it mentions vivid dreaming caused by melatonin. I have the "Melatonin and the Biological clock" pamphlet referenced in the article, and it does not go into too much detail of how vivid dreaming is happening.
I've personally experienced vivid dreaming side effects of melatonin today - dream after dream of profound intensity, but completely unrelated content. This makes me interested - how does melatonin influence the intensity of dreaming in humans? Is it by interaction with Serotonin? Or does it get metabolized into something psychoactive?