You don't risk dying from radiation if that's what you mean, but 2-3 days of eating crap food and drinking cheap champagne isn't any good for you. The recycled air isn't ideal either, especially if you're flying old 777-200s or their contemporaries with dry air which I know is more likely to give me some kind of cold at the end of a lot of flying.
Also don't underestimate the confusion the body will go through being denied the usual morning and nighttime cues.