It really depends on the rotation. I was pretty sick on my first rotation of the year--Surgery--and come hell or high water, I had to be there at 5:00am 6 mornings a week and stay till the end. Unless you had a very high fever or were literally vomitting or having diarrhea on the hour every hour, there was no way you could take a day off.
I've been sick on my Psych rotation. I went in, opened my mouth and out came my raspy voice and everyone was like "Go home. Leave. Why are you here?" I just took the one day off and slept all day which was very much appreciated. Honestly, if you feel like total crap, you're not helping anyone by showing up. You'll just spread it to the rest of the team and the patients. But if a resident or attending insists you show up, what are you going to do? Argue with them?