When I take melatonin, I sleep well, but I usually wake up in the middle of the night. When I don't take it, I take long time to sleep, but don't wake?

Melatonin. Melatonin supplements can help regulate the sleep-wake cycle by chemically causing drowsiness and lowering the body temperature. The fact that it's helping you to fall asleep but you wake up in the middle of the night suggests you may have some underlying medical causes for early morning awakening, such as sleep apnea or depression. You should avoid drinking any alcohol before bedtime. See a doc.