I have restless leg syndrome so I sleep for a little while then the jumpy legs wake me and I have to get up and walk around or stand then repeat. This usually goes on all night, I never try to go to bed before about 3AM. Yes I'm tired and grouchy most of the time.
I do try the relaxation yoga but sometimes I can't complete it because the creepy/itchy/crawling feeling in my legs means I have to walk. I circle the kitchen island, then the dining room table, the sofa etc., until I feel I can try to go back to bed, sometimes I just lie down and whoops no got to walk some more. The worst is if I'm sick with the flu or whatever when you have that feeling that you just want to crawl into bed but I have to stand. The biggest, absolute biggest luxury for me are those times when I wake up and I am just comfortable. It's like being cursed.
Four hours is tough. As an old shift worker I was used to going without sleep. I'm getting more than I used to but would love to manage your eight hours. :)