I rarely sleep for long periods of time, especially at the weekend. In the week I can quite happily stay up til 2am and get up when the alarm goes off at 6:30. On Friday I will usually not go to sleep until around 4am, getting up with the alarm at 6am. While I don't have much energy I am perfectly capable of driving and stuff like that.
Now, this weekend, I've had 2 (relatively) early nights. Saturday night I was in bed at half-past midnight until 8am and Sunday night I went to bed at 11ish and woke up BEFORE my alarm at around 6am. If I wake up prior to alarm, that to me says that I've gotten plenty of rest.
Why is it then that today I feel drained and nauseous!?