I have a 13-month old so I don't get as much sleep as I would like to. He is getting better with sleeping through the night, but he is also changing his eating habits (moving from formula to milk and solids) and sometimes he still wakes up at night to drink a bottle. I am not one who can nap during the day, and even if I could, I wouldn't have the time to do so.
I don't think one can make up for lack of sleep, it is just a matter of trying to keep your number of hours of sleep consistent if you can. I am not getting as much sleep as I did when I was 18, but I sleep about 5-6 hours per night on a consistent basis, and I think my body is acclimatized to that, to the point where any more or less sleep would make me tired.
As for depths of sleep, I used to believe that such a thing existed. I always thought I was a deep sleeper, until the baby came along and I heard him every time he cried out in his sleep, even from the other room. I do think that deep sleep vs light sleep may have something to do with if you dream or not. When I dream a lot at night, I feel like I slept lightly, when I don't dream, the opposite. :spock: