Promethazine
"I suffer from nightmares. At my doctor's suggestion I have been taking one Phenergan at night for many years. They calm my sleep and I have hardly any nightmares now.  I tried sleeping pills first but they made me feel as if I was in living in cotton wool through the day. I also tried Nytol but they made me hyper and unable to sleep! If I forget to take a tablet I will have nightmares that night. Have not had any side effects at all. Tablets available over the counter at the chemist."