I've had to get up before 6:30 AM the past couple of days, and will have to do so again most of next week. I wasn't able to get to bed before 1 AM either night (one night close to 2), and after two days of that I am worn out. Several years ago, I used to be able to last a few days with only a few hours of sleep each, but now I'm tired after not getting enough sleep on any one night. After two days of that I start to lose function towards the end of the day.
How much sleep do you need on any given night to be able to feel like a human being the next day?