There's a variety of herbal drugs for coping with medical problems but it hard to tell the good stuff from "snake oil." Now there's a graph to help determine what's worth the time. Having done quite a bit of research about getting good sleep, I've heard about Valerian Root for a while now but it seems pretty well received.
Low blood sugar meanwhile can actually cause nightmares. This sounds odd, but generally your body will respond to low blood sugar by having intense dreams. Then, once your adrenalin kicks in, it zaps your blood sugar almost immediately and then for the rest of the night, you will continue to have intense dreams as your body tries to tell you it needs energy (thanks switch). How you manage your own blood sugar is not a simple topic, but its something you should discuss with your doctor to handle restless sleep or frequent nightmares.
Some websites to help with sleep and some controversial software solutions (for Mac and Windows):