I had an issue like this with my gym teacher in high school. I was already pretty overweight when I was in her class, and some days I just had a problem with my ankles hurting and etc. She would accuse me of being lazy, even though I worked my butt off more than anyone else in the class, and improved my mile from 22 minutes to 13. But because I couldn't do it in 7, she criticized me. I just think people have this idea that overweight people are just lazy and looking for an excuse to get out of any physical activity, where if you were thin and said, "Hey look, my ankle is really hurting today, I must have strained it, can I just do a light jog or walk today instead?" she would have been like, "Oh, okay, sure."
But, it was my fault to let something like that bother me. I'm pretty sensitive, yet still over all of these years I still get upset remembering it when I should just get over it already. But all this time it just furthers my fear of people thinking I'm lazy. Who cares what people think? I know, easier said than done, but honestly, if you're doing this for YOU, then it doesn't matter what they think. Someday you'll be all thin and prove them wrong
As for me, I'll probably never see that gym teacher again, but I don't have to. It's all in the mind!