Sometimes others don't understand the illness. I personally believe that it is the responsibility of family members and close friends of someone with an illness to try to educate themselves on the illness, so they don't make stupid remarks like you described above.
I'm sorry they made that remark. Next time they do that, you should voice your opinion, say that you're glad they like it when you are well, but you really can't control how you feel all the time.
I'm glad you have had a good 2 days.