Self Confidence at Work

Something I've always noted being affected since my addiction started back when I was 11 is my self confidence. I've always been a quiet and somewhat timid person even before my addiction. But I've noticed since the addiction started I've had to work extra hard to push myself to do things. This has gotten better since my addiction started to get better five years ago. But I've noticed I still struggle with it quite a bit. I work in a gym and at times I see myself struggle to do my job concerning seeing if people who work out here live in the apartment complex. I tense up and start thinking about all the worst case scenarios. What is it about PMO that causes this?