How come when it's too hot during the day people feel tired, but when they try to sleep at night, it's too hot for them to sleep?

Metabolism: Our metabolism believe it or not, goes UP during sleep. Frequently, our body temperature will rise slightly and can cause some sweating while we sleep. During the day, when we are more physically active, a number of factors play into how we feel tired or overall energy level including humidity, dehydration, muscle movements, ambient temperature.