I used to take melatonin regularly, but after I got a concussion I was informed (finally) that taking melatonin can inhibit your ability to sleep without it even more than that ability was already inhibited.

Which is probably worded badly but whatever. I only ever had nightmares when on Aleve, but I know I was taking too much of that because a few days later I got really sick from the Aleve. Nowadays I take GABA supplements, and Benadryl if I'm really worked up.