I have a hard time believing that anyone can sleep for just 4 hours a night and be completely attentive for the whole day. These days I almost regularly sleep

I have a hard time believing that anyone can sleep for just 4 hours a night and be completely attentive for the whole day. These days I almost regularly sleep only 4-5 hours a night and I "can take it" but sometimes during the day I practically almost pass out from the tiredness - that passes shortly though and just closing my eyes for a bit helps a lot. And I yawn a lot but then again I do that even if I sleep for 10 hours or what have you.