For many sufferers of ME, not a lot!
I find there are two primary difference:
It gets Dark at night and not so much at day time and, there are fewer people at night.
What makes me decide to go to bed?
Lack of anyone to interact with. In short, I get bored.
How do I feel at 2am (as it is now)?
Tired but, no more tired than I felt at any other point. No, that’s not quite true, I do feel more tired but, it’s tired upon tired and I cannot think of a better way to describe that. I sometimes feel this way at 2pm so, it’s not really dictated by the time of day. Feeling this way at 2pm could just as easily happen if I have a week of 7 hour sleeps.