As long as I feel refreshed after a sleep I deem it okay. It does not matter to me if I slept for a total of 10 hours or just 3. There are times that even if you already got plenty of sleep you still feel very tired. I guess we need to listen more to our body to see if we are getting enough rest or not. Enough sleep is not the only thing that our body needs; we also need to be aware of our diet and activities. However, we cannot argue that sleep is very important since our body need this time to regenerate itself.