How do you tell if you have slept well?

Question: How do you tell if you have slept well?
- Keywords:
  sleep
Asked by mrinsanet to Asif, Laura, Lena, Sean, Viv on 19 Mar 2012. This question was also asked by abutler.
- Lena Ciric answered on 19 Mar 2012:
  
  Good question! The simple answer is – you wake up feeling good and ready to face the world. I’m afraid I don’t know the technical answer – I think you need to have a certain amount of uninterrupted REM (rapid eye movement) sleep, though.
- Sean Murphy answered on 19 Mar 2012:
  
  Personally the degree that my hair sticks up tells how much sleep I had. Different people require different amounts of sleep. Studies show that people who sleep between 6.5 hr. and 7.5 hr. a night, as they report, live the longest. And people who sleep 8 hr. or more, or less than 6.5 hr., they don’t live quite as long. There is just as much risk associated with sleeping too long as with sleeping too short.
- Viv Lyons answered on 19 Mar 2012:
  
  How good I feel and how clear my thoughts is normally my way of telling.

Question: How do you tell if you have slept well?