Well, you can be sure that J cares about you, since J emailed to see how you were feeling after your procedure.

Maybe nobody invited you out because they thought you needed rest after your procedure? Maybe they knew you already had plans to see the art show? Maybe they were going to an event that they thought you wouldn't enjoy? There are so many reasons that people might have for not inviting you out, and most of them aren't personal.

Concluding that you weren't invited out because of some personal reason probably did make you seem like you were accusing people of something. Sometimes it's best to keep one's hurt feelings to one's self until there is more concrete information available. I know that hard, though, especially when you're in a delicate state. Sorry that you don't have a more compassionate friend.