It's been known for quite some time now, centuries, maybe millenia, among people practicing intensive meditation (monks, basically) in many different cultures a

It's been known for quite some time now, centuries, maybe millenia, among people practicing intensive meditation (monks, basically) in many different cultures and religion, that mild sleep deprivation (really, just keeping sleep at a minimum without impairing normal functioning) acts as a safeguard against depressed mood. It's a constant advice in many different schools of meditation: "don't sleep too much, keep your sleep duration at a minimum, wake up early, and meditate".