People with many mental health conditions use gyms or a variety of other things to keep their condition under control. You may not turn into a nervous wreck but that doesn’t mean they won’t. They may get anxious as the gym is the only place they can exert or that it’s the only place they meet some like minded individuals, take part in classes for example. So I’d suggest you stop thinking that how you’d react is the same for someone else and especially take heed of what you posted earlier in being kind to each other, if you can’t, then yes, you’re confirming that you are indeed a twat.