Melatonin produces really enjoyable lucid dreaming at the right doses. I found out the hard way that too much is a big mistake. So I started taking about 4 tablets 3mg melatonin each night, but no dreams occurred. Then I took 6 tablets (18mg) and only little dreaming happened. I kept upping the dose, then I found the right amount, on 30mg melatonin I had great dreams, but unfortunately extreme drowsiness was a big downfall.
After 2 days taking 30mg, I felt horribly sick in the morning, it would go away, then would come back worse. Every day I would take antacids, but that wasn't my case. I stopped for a week then I took 36mg (12 pills). I felt so much nausea and dizziness; I couldn't even go to school that morning.
So then I stopped for a couple of weeks, until a night I just couldn't sleep, so I just took 3 pills. I thought that wouldn't disturb anything. I woke up after having a dream I was sick, and then vomited my guts out.
Now my system cannot at all handle melatonin at any dose. Apart from the awesome dreams it can produce.