I think because it's so quiet and there's no other distractions. Can't look out the window and even "see" the weather/neighborhood so there's more of a feeling things are closing in on one too.

I have a "kit" for nighttime. If I can't sleep, I do lights, special foods, special books and music, PC and other online places, etc. Usually I feel sleepy or a bit better by 3:00-6:00 (depending on when I've gotten up) and can go back to bed. When I worked I just tried to wait it out to at least 5:30-6:00 and then had the treat of an early morning instead of being rushed. Sometimes I like the quiet in the morning and working in my journal or on a project. I use to get unhappy when I actually had to get ready and go to work. But on real bad days I had special music I'd play in the car on the way to work and/or I often would get special books on tape. I'm better at work when there's stuff going on and I'm expected to do stuff.

One thing when I'm alone too many hours, I make myself go out during the day to make sure I've talked to someone in person; librarian, clerk in a store, anyone. I found if I don't do that (stay in all weekend) then I just get really weird :-)