Define feeling sick.
Are you getting the same amount of sleep as you did before, just with changed times ? How long have you been on your old schedule ? Could be your body needs to adapt, but i am not sure.
I know that if i go from sleeping 8 hours to only 6 hours i feel exhausted, i wouldnt call it sick though, just really tired
Could also be you just coincidentally caught a cold at the same time.