Without a doubt. However, suddenly "becoming" sick the second after you got tagged for an assignment is pretty much indefensible. It's obvious that in 99.99% of all such cases the person involved was just punking the system and got caught. Unless you're going to the emergency room and have the proof of why you need to go and go at that exact moment, you best not try that strategy. If you are becoming sick on reserve you need to call them first rather than busting out a "oh yeah, about that...." once you are tagged.