Let's get straight to the point.
If you want enough sleep;
Age 20 and below, sleep 8 hours.
Age 21 and above, sleep at least 6 hours.
If you sleep 3 hours, wake up and sleep back
another 5 hours, that would not be the
same. Still be considered as lack of sleeping.
That's why, some people says that they have
already sleep "accumulatively" for 9 hours
but still sleepy.
Try to sleep continuously, if you have trouble
with it, try to do some sports activity.
It doesn't have to be heavy sports. As long
as you move your body and sweats.
Ok that's all for now.