I've been on a midshift (11a to 11p) for 2.5 months now after working nights (old-fashioned straight-up 7p to 7a) for years. I have decided it's about as difficult to switch from nights to days as it was the other way around. Maybe it's because I'm older now and more set in my ways, or maybe it's because when I started working nights I was in nursing school and never slept anyway, but whatever the reason I have not adjusted quickly or well. I was able to sleep at night right away, probably because I like to sleep and have always been a good sleeper. Waking up was a bigger problem, but it turns out I hate waking up regardless of the time of day or night. I don't think sleep is my circadian issue; I think it may be food.
I just can't figure out when and what to eat. I used to wake up in the afternoon, eat a lunch/dinner kind of meal, snack all night at work (consuming actual food at 2AM makes me queasy, and yes, I realize that makes me an anomaly), and eat breakfast when I got home before going to bed at 8a. Now I get home around midnight, and I've tried eating a meal (lie in bed feeling like I have a ball of food in my stomach --> queasy; NNR does not eat in the middle of the night EVER, apparently), not eating a meal (wake up frakking starved and feeling half-sick with stomach pains), and eating a snack (unsatisfactory in-between results). My body does not like any of this.
Also, I've gained weight despite no increase in food intake and a considerable increase in gym visits, which pisses me off because you're supposed to gain weight when you work NIGHTS, and I've had zits ever since I switched shifts. I have always had clear skin. The final awesomeness is that nearly every time I fall asleep I have weird dreams up to and including nightmares, and I have never been much of a dreamer. Until the last 3 months I'd had maybe two nightmares my whole life.
In short, the change is not going as I'd hoped. It's actually been rather catastrophic. It's brought other hoped-for changes, so I'm persevering with faith that my body will work itself out somehow, but holy cow!