Most people have been taught that exercise is a cure for lethargy. For certain types -- frex, oversleeping -- it actually works. But most of the time it just makes matters worse.

Try telling people you don't feel well, or even "I feel like I'm coming down with something." And don't go into any more detail than that. Then they'll be more likely to encourage you to rest and take care of yourself.

Some physical challenges, people just won't accept. Work around it. You're unlikely to change their minds.