I have no idea what caused it.. but when I would have it, it was sometimes the type where it felt like someone/thing was coming from behind me and holding me down or sometimes I was drowning in a pool. The melatonin always made me feel like something was holding me down. I never saw anything strange, but always felt creepy while it was happening. I don't believe in ghosts or evil spirits, so it wasn't traumatizing lol just at the tine it was happening.
The melatonin always made me feel like crap the next day.