To me what really matters is not how many hours of sleep I get but how difficult it is for me to wake up. I've found that there is a direct relation between this and my happiness.

In periods where I am very productive, I have a reason to wake up, I know what I want and need to do. Then I'm very happy, life has a purpose. It doesn't matter how many hours I sleep.

In the other hand, when I amb lost and don't know what I should be doing that day, I have a very hard time waking up.