Depends on what's going on. If I throw up that day, all the moving around from having sex doesn't sound too tempting. If I have endo or cystic pain there's no way in hell I'm having sex... period cramps and the usual nausea I can deal with and will soon forget when having sex. If I have a cold we won't kiss and I'll try to stay sexy as possible as I stop every minute to blow my nose.
If you have body aches- start off with something like the Heart Massager or a massage and go from there. If you start to feel better or really want it than be receptive- if he knows you're feeling weak than request oral.