Why can't I Sleep?

So, I worked my hind end off yesterday (and all this week actually) and I didn't nap, didn't load up o caffeine. We even went swimming in the evening so I could relax my muscles - and amazingly, I'm not sore or stiff this morning! I went to bed at 10:15 and fell asleep within 10 minutes I would say. But... Henry woke up at 2:30 am for a little bit, and I couldn't go back to sleep. I tried for half an hour, then got up to go to the bathroom and came downstairs to read for about an hour. I went back upstairs a little after 4 am and still couldn't sleep. I was FINALLY feeling myself drift off sometime after 4:30 am and Henry woke up at his usual 5 am... I'm not getting more than 4-5 hours of sleep ANY night and working HARD all day every day, so what is the deal!?!?! Did Henry's first two years of waking 5-7 times a night condition me to not needing sleep? I know I need it because I'm always in a fog and my brain really doesn't "fire" right, if you can understand that? I just don't get it! I should have slept HARD all night long! And now I'm afraid I'll have to take a nap with henry because I can't POSSIBLY be able to sustain this lack of sleep indefinitely. Sigh... What is WRONG with me? An opportunity to sleep and I'm up half the night???