Yes 4 hours of sleep is bad for your health.
Getting 4 hours of sleep is much better than getting no sleep or only an hour or so of sleep but you should really be getting at least 8 to 10 hours of sleep for the best health.
Sleep is a very necessary thing for our health and well being and to keep us alert the next day and sleep also helps us to function properly.
Lack of sleep can lead to heart disease, heart attacks, strokes etc.
Lack of sleep also causes accidents and especially when driving as you're not very alert when you lack sleep.
So aim to get at least 8 hours of sleep at night and more if possible.
I get at least 8 hours of sleep on the weekdays and on the weekends when I can sleep in longer I try to get 10 to 11 hours of sleep.
I feel much better when I get at least 8 hours of sleep but I feel even better when I get 10 hours of sleep.