I kind of have to contradict the "naturally diurnal" thing. My natural sleep schedule as an adult is going to bed around 2am-4am, and waking up at about 11am-1pm. I tried to change that for more than three years while I was with my ex-husband, and it just didn't work- I was grumpy, tired, listless, and generally felt very unhealthy.
Unfortunately, society seems to assume that most people are the daytime-type, and I get classes that start at 10am, or have to work around that time, too. It's very frustrating, and I often describe it as "Imagine if you had to get up and work at 4am. You wouldn't be happy, either!"
I cannot sleep before 2am. I've tried. I have REALLY tried. My best sleeping time is actually between 5am and 11am. I get the highest quality sleep then.
And that's where the issue is- when you don't get that highly efficient, truly restful sleep, you'll suffer. Loss of energy, focus, and motivation. You may be getting a full 8 hours of sleep, possibly even more, but it won't be the same.
My suggestion would be to make sure you're eating often, and perhaps more than you would consider to be "normal" for you. Not too much more, but a bit more. Remember that you're trying to replace energy that you are lacking from not being able to sleep at your ideal time.
And, if you feel that this sleep schedule will be going on for longer than a month, don't deviate from it, even on weekends. It's really tempting, and it can be really hard to just stay tired when you know you have time to sleep... but you may be able to transition your body to your work schedule. You suffer for the first bit, but I'm told that most people find it gets easier.