I've been sleeping from 1:30 AM to 6:15 AM on weekdays and at least 12 to 14 hours from Friday to Saturday and Saturday to Sunday. Been doing it for 4 years sin

I've been sleeping from 1:30 AM to 6:15 AM on weekdays and at least 12 to 14 hours from Friday to Saturday and Saturday to Sunday. Been doing it for 4 years since I changed schedule. I don't feel tired or impaired at all. Usually able to start working around 7:30 AM (feel really sleepy before that). Recently (couple of weeks) had a shift and now stay up to 3 AM on some days and catch a 1 and a half or 2-hour nap around 5 PM. I feel tired and impaired after waking up. Only get back to normal the other day. My sleep is determined by the fact that besides a full time job, I'm pursuing a Doctorate and consistently try to get solid 9~10 hours of work+study every day, with 14-hour workdays every once in a while. The amount of work I do or effort that I spend has absolutely nothing to do with how much or how well I sleep. The amount of exercise I do, no matter how little, has a great impact.