Life Down On The Farm

In all the years I have been working I have never had a performance review. Today I am having my first one and I AM FREAKED OUT!! Is it possible to have a mental breakdown from this? Because I am well on my way. I know it will be okay, and I know any criticism will be constructive, but I take my job very seriously and having my boss tell me what I am doing wrong is going to kill me. I have already told him I will walk out of his office feeling like a whipped puppy so he shouldn't take it personally. I really like my boss and I know he appreciates what I do, but I also know he is going to have fun with this evaluation, if for no other reason than to torment me, but I am so nervous I could pee myself. I am doing a good job, I am helping, I am an asset to the company...I just need to keep telling myself that over and over and over...