When I find myself in a situation were I am thinking negatively or am anxious, I ask myself a simple question, and quite a few times I have found that my anxiety eases. The question is as follows:
"Will this matter in 5 years"?
I say 5 years, becuase your life situation is likely to have changed substancially enough in that time, that what you say or do now won't have an affect on the future at that time. Also other people tend to forget what you said or did in that time too, so you don't have to worry about people remembering or bringing up old issues.