A Question for Humans

I don't get the whole concept of the cat nap. You sleep for 20 minutes and then you hop up and you're good to go? Never in my life have I been able to do that. First of all, it takes me at least that long to fall asleep (usually longer). Second, if I nap I want to nap for a couple of hours at a minimum.

So what's the deal? Are y'all just lying there awake for 20 minutes, and that's enough to refresh you? How does this work? Does not compute, need data, beep beep.

(Koff. I could, uh, use a nap, obviously, but have no time to spare.)