The reason is you feel bad is you should not go to bed when you finish work straight away. You should come home and relax for about 4-5 hours. Go shopping, do some housework, or just watch t.v to get yourself relaxed. Then you go to sleep. You do not come home from work in a normal day job and jump straight into bed. You have a few hours to relax, have some dinner, watch t.v then go to bed. I saw this on a programme so I am not talking out of my backside here. It showed this is the art of doing nightwork and it makes sense doesn't it? You feel feel more relaxed and sleepy by the afternoon after watching all this day time t.v and will easily fall asleep and wake up more refreshed hopefully. 12 - 8 = 8 hours sleep. This leaves 2 hours to wake yourself up and have some dinner before starting work at 10pm.