How do YOU feel?
I know I'm getting enough sleep when:
- I wake up BEFORE my alarm clock goes off, or on the first beep
- I am not constantly seeking sweets during the day
If you are pushing yourself out of bed, drinking a pot of coffee, drinking caffeinated soda and then still feeling tired you aren't getting enough sleep.
Generally, you can't "make up" sleep by going longer on the weekend -- get that sleep during the week consistently and you will do better.