I had pretty bad insomnia about two years ago. Even now, I have a hard time falling asleep, but I've finally gotten back to the point where I stay asleep once I've fallen asleep. I always end up waking up super early though, and I never feel quite rested no matter how much I sleep, though I have my good days.
It could be some kind of anxiety, but not necessarily enough for a full diagnosis. Many people think/process too much before they sleep. It's important to clear the mind before bed. Since a lot of people seem to have insomnia here are some hints:
1. If you take medications (prescription, OTC, or herbal) take it 30min-1 hour before you go to sleep, and wind down while the pills take effect. This usually involves laying in bed and preparing for sleep. Don't do anything active for mind or body.
2. Find a relaxing distracting before you sleep. With some people its reading, others its something like applying lotion. Some people meditate. Try to avoid things that really exercise the mind (like puzzles, philosophical thoughts), those are morning exercises.
3. Deep breathing exercises help as well. Your mind and body need oxygen. Without healthy breathing humans can't reach a calm sense of being. You can practice inhaling up to 8 seconds and exhaling up to 8 seconds. Focus on your breathing, picture the air entering and exiting your lungs.
4. Stay away from music before you sleep. Getting a rhythm in your head before sleep can be very disruptive.
Some good herbal sleeping supplements are Valerian Root, for those who don't like prescription drugs.