Again the triggering point was our own experienes and their comparisons.Iwould share my personal and fairly recent experience.When I used to sleep 6 or lesser hours with 3 hours of sports and a good amount of study, I used to feel more energetic than currently where I am sleeping more than 8 hours and not having any physical activity with teh same amount of study.Today afternoon he was having extremely delicious and food 'Khakhara' with high quality 'ghee' on it.And even though hungry , I was so lazy to even get out of my bed!!I could't believe that a food lover like me can be so ignorent of 'Khakhara' just for sake of rest!!
Anyway ultimate inference was try not to sleep more than 6 to 7hours be cause sleep after that follows positive feedback mechanism.The more you sleep more you feel like sleeping!!