Nobody can sleep for 4 hours per night, that's not enough for your brain to rest.
Better find a new job because such conditions could harm you. Personally, I think that's individual I mean sleeping for 7-10 hours. You should ask your parents how much do they sleep and try, well, the same hours.
The sweet spot is usually 7 hours; sometimes your body will "wake" you up even if you don't set any alarm
7 hours is so little for my body.
If I am tired and I sleep only for 7 hours then it will be very hard to operate during the next day. My body usually requires 8-10 hours of sleep in order to be fully functional.