Yes started when i was working and studying, up at 7.00 am start at 8.00 am, finished at 4.00 pm run like hell, start work at 4.00 pm, could finish work at 4.00 am, working and doing homework at the same time, go home quickly stuff food in my face because shops in the city start closing at 5,15 pm getting food was a pain, then i would fit some sleep in, and start again. After that my internal clock never reset so im pretty much awake all night and sleep during the day, ive done everything that medical people have told me and nothings worked, every time i try and change the time i sleep it just goes back,
In your case it probably more that now you have no need to wake early your just getting used to staying up till late, and thus end up sleeping during the day, but since youve already been in a pattern of having to wake at a set time for work, when you start work again you will just fall back in the same routine.
If you desperately dont want to sleep during the day you can skip some sleep and make yourself tired, or just do some hard physical exercise and start setting a time at night to sleep , that is pretty much what doctors tell you, or you can wait till you get another job feel crappy for awhile as you sleep patterns reset. But as a recommendation from someone who's seen this happen to alot of people, most of them just fall back into a normal routine, a few dont and end up struggling with sleep problems.