Another issue to look at is quality of sleep. If you have apnea it can totally wreck the quality of whatever sleep you do get. I used to sleep 8 hours a night but still always felt tired. I also had a serious case of sleep apnea. I could fall asleep just about anytime and anyplace - in fact NOT falling asleep anytime I sat still was a struggle. Once we resolved the apnea issue, 8 hours a night is more than enough sleep and I am not nearly so tired all the time. I actually have to
try to fall asleep most of the time - including if I want to take a Sunday afternoon nap