Sleep Deprivation

I read somewhere once that the primary caregiver of a child loses over 700 hours of sleep in the first year. Since you also lose sleep when you're pregnant, and I have 4 kids, I figure I'm thousands of hours behind. How can I be expected to function without forgetting at least something?

Here's an example. Last night I had my 2 middle children in bed already. I sat down in my recliner to nurse the youngest and the oldest had just gotten out of the shower. I sent him to bed and told him I'd be in to sing him a song as soon as I finished nursing the baby. I finished feeding her, put her in her crib, and started doing something else. Half an hour later, Frugalboy comes out giggling, "I've been reading for a HALF HOUR, MOM!" I totally forgot to go in there. At least he was doing something quiet and intellectually stimulating.