Am I the only one who's more tired if I get greater than 5-6 hours sleep?

Over a lifetime all you ever hear is “get a full 8 hours sleep” but I can barely function the next day if I get more than 6. Now occasionally I’ll sleep for 10–12, but that’s typically once every 2 weeks or so.

I will note, however, that when I fall asleep I’m pertty much in a coma. I’ve been told that I hit R.E.M. sleep almost immediately, so at least I’m using every minute of my time.

Basically I just want to make sure I’m not shortening my lifespan by only getting 5–6 hours of sleep per night over a LOOOOOONG period of time (like years.)