Q: Is six hours of sleep at night enough?
…Six is the minimum, at any time except in old age. The ordinary period of sleep most people give themselves is 8 hours. In bad health (I am not speaking of acute illness) it can extend to 9. 12 hours is excessive unless one is seriously ill or recovering from illness or else has underslept for a long time and the body is making up arrears of needed sleep. There is no reason at all why intensity of sadhana should bring insufficient sleep.
– Sri Aurobindo