I worked nights for 2 years in a factory, and am just about to start my first LPN job on nights. I can tell you from experience that if you look out for your 2 main needs of sleep and food, it can make a big difference in how you feel.
I worked with a lot of people on nites that didn't eat anything their whole shift!! I just could never understand this! Your body needs fuel! For you, it might mean a little snack with some protein to get you thru the last couple hours. Personally, I would bring in a lunch to have at about 3 or 4, then a granola bar or something for later.
And don't neglect your sleep!! When on dayshift, you would expect at least 6 or 7 hours of uninterrupted sleep at about the same time each nite, right? Well, same goes for day sleeping! Go to bed at the same time every day if you possibly can, and remember that 3 and 4 hours at different times is not the same as 7 hours in a row!
as for packing on a couple pounds, that happened to me too. right after the darn place installed vending machines! :angryfire
Yah, I had mood swings, too. More so on my days OFF, actuallly.(due to sleeping differently)-- I just started taking melatonin...we'll see how that works out.
luck to you!