This is something that's really important. We need society to realise that being ill or disabled does NOT necessarily mean you use a wheelchair or walk with a stick. Illness such as M.E. Lupus and M.S. are all examples of invisible disabilities.
http://www.butyoudontlooksick.com/
http://www.chronicfatiguesyndrome.me.uk/
http://www.ukfibromyalgia.com/index.html
http://www.facebook.com/pages/The-Spoon-Theory/356153177497?ref=ts
Not all disabilities are visible - it doesn't mean they're not real.