When I used to work nights, and now doing 24's, the body can never set it's rhythms. I always hit a wall right after noon (I wake at 0400 and leave the house at 0430), and my body "comes alive" from around 1800 to 0100. This means that I'm dragging during the early to mid afternoon every day, and I can't seem to fall asleep before 2300-0100 in most cases, unless I'm really shot. I try and get some sleep in the afternoon at the station. Some have made comments about that. I point out that on the ambulance, I can be up several times a night, typically for an hour and a half each time, unlike them who either run two calls a day on the truck, or are back in bed in a half hour or less when on the engine. My time spent up is certainly more than 16 of the 24 hours I'm at work; if I need to get some sleep earlier in the day, provided all the FD stuff gets done first, I'm going to do it.
After pulling an all-nighter on a 24, some say to just stay up all day after coming home, and just go to bed early. It doesn't work. You're just miserable and useless all day, and your weekly sleep totals still run in a deficit.