Sleeping and Waking up
You need at least 6 hours of sleep every day to keep functioning at your best. If, at the end of an extended rest, you haven’t slept at least 6 hours in the last 24, you gain no benefit from that extended rest.
When you’re asleep, you’re unconscious. You wake up if you take damage or if you make a successful Perception check (with a –5 penalty) to hear sounds of danger. An ally can wake you
up by shaking you (a standard action) or by shouting (a free action).
Published in Player's Handbook, page(s) 263.