For some it's easier to be comfortable and 'themselves' than around people who know them. I have that issue. I struggle most with people I know. I always feel so much pressure to be a certain way - do well, be well, be doing really great constructive things with my life - and I feel so self conscious most of the time that it only makes me more anxious and depressed than I already am. Plus people in my life tend to be biased, want the best for me, have seen me at stronger moments in my life, and so just can't understand why it is that I can't just 'decide' to get better, or 'get better faster', or whatever. Some of them just plain forget that I have MI at all and act like I don't and I have to constantly remind them whenever things come up that trigger me.
Anyway. That's just me. It's easier to keep a safe distance from people close to me.