[bunderbunder]

It varies by person.

I think it also varies for a person. My rule of thumb is, I don't want to make a habit of having my alarm clock be what wakes me up. For me, that means that sometimes I'm up and moving less than 7 hours after my head hits the pillow, and sometimes I'm still sawing logs 9 hours later.

Stress seems to be a factor. Which, ironically enough, means that the more I sleep, the less I need to sleep.