Melatonin is a double edged sword. It helps with some symptoms of jetlag, and yes, it’s involved with sleep timing, but taking exogenous megadoses isn’t the same as your own production. A bit like screwing with exogenous EPO; much better to let your kidneys take care of that for you, IMHO.

Exposure to light, or lack of it, seems to have a big effect on sleepiness. Certainly works for me – so I try to be careful about reducing light exposure at night, and waking up with plenty of light.