After a trip i take 3 mg's Melatonin, some Kava Kava, Valerian, and 5-HTP. The Melatonin will knock you out in 15-20 minutes.
Sometimes i don't take it, thinking i'm tired enough from dancing and making love, and i'll keep laying in bed and as each hour goes by i keep wishing i took it, then eventually all my friends that tripped with me are waking up and now my day is going to be spent in a haze.
I'm not sure if Melatonin is synthesized or made from animals, but if you're vegan you might want to do some research. It can be found in any pharmacy in the vitamins and supplements section.