I give you permission to tell your friends that you don't want to risk a headache to spend time with them.
You'd choose differently than I would, apparently. Having tried both approaches to dealing with the situation (with other groups of people), I've decided that I prefer this one. You can take your condescension and shove it up your ass; it serves no useful purpose here.
> At the risk of channeling $STEREOTYPICAL_MOM, are people who'd ask that of you really your friends?
They don't know, because I don't tell them. Otherwise, they'd bend over backwards to accommodate me, which would make me more uncomfortable than the physical pain does.