OMG I didn't read this post till just now, but man that sounds like me too. I've read articles about IBS before and they always tend to think that people with this kind of personality are more prone to IBS because of the anxiety and stress and worry they feel so much of the time.
But anyhow I too get labeled as being shy, but that's not really the case. And especially apparent to me now during the holidays when we have been invited to do stuff like every other day, but I'd rather just stay home by myself and read or something, no matter how much I like the people we'd go to see. It's weird cause I feel like people will think I'm lazy, but it's definitely not that. I'm just happy to be alone like that.