Yeah, I noticed a few years ago that I had bad insomnia that came and went - separate from the pregnancy insomnia that plagued me during the first and third trimesters.
After paying attention to it a few times, I noticed a few things:
1. Stress-induced insomnia from work
2. Hormonal induced insomnia. I noticed that I don't get it every month, but when I do, it's 3 days, and it happens when I am ovulating (sorry if TMI, but this is, in fact, why we have a second child. Because the first night of insomnia I went to the gym at 3 am. The second night I didn't.)
I've worked really hard over the last couple of years to reduce the work-related stress as much as possible (in my office, this is VERY difficult). I also simply started taking Unisom nightly - this allows me to fall back asleep within 1/2 hour instead of being up for 2-3 hours.
I'm in a bad hormonal spell right now (don't worry, no third child) AND a bad stress spell AND I have a cold AND my toddler was sick last week. So I had a few days of bad sleep from the toddler and it just rolled over to the bad hormone streak. So the last two nights I didn't sleep well and didn't even fall asleep until after midnight 1 am, despite the Unisom and the Nyquil for the cold. It's some stubborn stuff. And it's annoying. At least I know that at worst, I only have one more night.
My neighbor up the street (two of them) are women in their 50's who have insomnia also from 1 to 3 am or so every night. They just get up and do things and then go back to bed. That leads me to believe it might be somewhat "natural" to our bodies (and maybe even hormonal). I would totally do that and not stress about it if I weren't working 8 hours a day.
As it is, I figure I can handle a few days of no sleep. I really try to sleep and force it, but last two nights I just have been reading. Other times, depending, I may knit/ crochet or yes, go to the gym at 3 am. Our house is small - if i could figure out how to get out my quilting gear or cook without waking everyone, I would do that. I figure I might as well be useful if I'm awake. I would have done work last night except I don't bring my computer home anymore. Maybe I should do PTA stuff. Hmmmm.