system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is that technically too much sleep is bad for us?
gpt
Your muscles need stress (exercise/movement) to stay strong. If you stay in bed all day your muscles decide they aren't needed and go away. Same for bone strength. Your bones will literally be easier to break. 

Also too much sleep throws off your sleep schedule. Having a consistent schedule is best. Trying to get extra sleep on the weekends doesn't work too well. 

If you try to get extra sleep one day you might be in deep sleep (rem phase) where if you wake up in this phase you will feel very tired even if you were asleep for longer than you normally were. This is also the case for naps. If you enter a deep sleep and wake up in the rem phase you will just feel more tired. You need to wake up when you are out of the rem phase. 

A consistent schedule will make sure you are out of the rem phase of sleep and you will wake up refreshed.