We're never allowed to miss clinicals, not even 1 day. If you're really sick and have a doctor's note, then the clinical day can be "excused" and you will have to make it up during the make-up days at the end of the semester.
This semester was the first time I've really been sick to the point where I didn't think I would be able to make it through clinical. I ended up going to clinical anyway and then I was sent home early. My instructors were great about it and aren't making me make it up, since I was there for most of it and was able to get my careplan done.
I think it just really depends on the school as far as how many clinicals you can miss, but for the most part you can't miss many, if any at all. I think they are highly regulated by the state BONs as far as how many clinical hours students must have, and in order to be accredited they must abide by that. So most schools will probably be strict in their clinical absence policy. I think the best thing you could do is just talk with them about it, share your concerns. Talk with your doctor, see what he/she recommends. Good luck