Yeah, sleep is pretty important for your health, especially mental. I'd list some symptoms, but I'm sure WakingDream's post has it all covered. Overall though, insomnia is not good for mental stability. My theory on dreaming is that it works as a sort of defrag program by running all the days information through your head and organizing it into stories and events to make sense of it all and keep everything stored in an organized fassion.

I'd recommend getting some melatonin. It's a sublingual (under the tongue) hormone you can buy at any health food store. Melatonin is responsible for making you sleepy and relaxed, not to mention i helps destroy cancer cells, and your body produces it naturally to fall asleep. If you can't fall asleep easily, you most likely lack melatonin.
An interesting note too, smoking weed causes a 5,000% inrease in your melatonin levels. This is largely what causes the initial relaxation and sedation, and is especially responsible for the burnout at the end. I have a strong suspicion, though, that the increase is much more mild when your tolerance goes up since experienced smokers tend to not be so heavily sedated. Heck, when I get high I feel more inclined to go out and do stuff, or walk my dog or work out.