Pulling the Chronic Illness card

If I wanted special treatment, I could make a really good case for it.
[my chronic pain, lung, and immune system issues make it hard for me to do things]
but I think there is a time and place for using your extra get-out-of-work free days due to chronic illness.
The other day I was supposed to go shopping and then to Mass with my dad but I had to call him to cancel because my joint pain made it hard to even get across the hall to my bathroom. I rested, called my doctor, and took some medication and felt better by 7pm. At that point I felt well enough to do things, and went to play video games at my friends dorm.
This is not a boy-who-cried-wolf situation, like the kid going to a sports event with 'the flue'. I HAVE joint issues and I did the things im supposed to do when I run into these problems. I think that justifies canceling on my father but still playing games with a friend. Whats the difference? The word “Chronic”.
Somebody experiencing more acute joint pain might take a whole week off of work for what I experience on a daily basis, and that's because its WORSE and ABNORMAL to them compared there typical illness. But on the other hand, I have a tendency to push through things I maybe shouldn't because if I took a day off for every new discomfort, I would never get anything done. And I cant tell you how many times ive missed events that I WANTED to go to.
The statement “but you don't look sick” is honestly the string of words that pisses me off the most in my life right now. There are days that I am in so much back pain that I can't hold down food and people tell me “you probably just ate something weird.” it might upset me more then it should but it is frustrating that most people will never understand chronic pain/ chronic illness unless they have experienced its unpredictability.
So what am I saying here? Cut me and other chronicly ill people some slack, we know our bodies and our illnesses better then you do. Dont worry.
Also, dont use your mild asthma as an excuse to sit out in gym when I did it with undiagnosed/ treated chronic upper respiratory distress and severe asthma.