Is there a point of diminishing returns? Everyone is different, however, is there scientific evidence of excessive sleep leading to poor physical and cognitive performance? Personally, I average 9.5 hours of sleep in the winter months, and 8 in the spring and summer. I feel much more energized during seasons of less sleep, however, I think it is just a correlation since I prefer those seasons. Has anyone ever felt like they were less energized/flat when they overslept? Any sleep hygiene recommendations for too much sleep?