I was just thinking about this last night. I was so exhausted that I fell asleep on the couch with the lights and tv on and the cats running around. But when I moved to the bed in the quiet, dark bedroom I couldn't go back to sleep.

For myself, I think most of my sleepless nights are due to stress. When I do lie awake I am usually contemplating things that have happened or will happen at work. When I'm exercizing regularly, I sleep much better.