3 hour sleep time is not enough for your body and you will not feel freshness in whole day. The chances of getting trouble will be increased. At least 8 hour is necessary for you to give rest to your body.
You only sleep for what is required of your body 3 hours a night no problem that's all you need other people need more at other times when you're sick you're require more sleep but normally a few hours no problem
You should have 7-9 hours of sleep. If you don't sleep for long enough it can cause you to get hypo when you're extremely tired. It also causes you to eat more calories in the day too. If you have trouble sleeping go to your doctor. It's not good for many reasons it will affect you're health.