((ABS9988)) - I agree they shouldn't assume your silence or lack of emotions are "coldness". Maybe your illness is making you numb or you might not be comfortable showing emotions for what ever reason.

I'm thinking they're expecting something, so when they don't get it, they assume the worst. When I was younger I was painfully shy and sometimes people would refer to me as 'stuck up' which was so far from the truth - I was just too shy to respond to or approach people.

It would be good if you could tell them not to assume you're cold. Stick up for yourself or maybe tell them how you're feeling.