Oh biscuitmuncher, I’m so sorry to read of your experience. You are definitely not a burden. Heat can affect some people with arthritis in the same way it affects others when it’s damp and/or cold. Shame on the individual who made you feel like the biggest s**t going. It says a lot more about them than you.
Take care, and next time, say “no thanks*.
Sometimes, I think some ( by no means all) younger folk and some (again, not all) older folk who are fortunate not to suffer health issues, don’t realise what it can be like to be coping with debilitating conditions (whatever age the sufferer might be), and that one day they may be faced with the same or similar issues. They should count their blessings but not denigrate those who are suffering.