Is it normal that i work myself up for upcoming events?

One of my coworkers/friends asked me to come to a party that they're throwing at their house this weekend. I said I would go, but this whole week I've been stressing over it really bad. He said that he's having a lot of people come over from his hometown, and that there's going to be a lot of other coworkers from other departments there too. I don't really have a problem with that. I'm just thinking of the "what ifs?". I haven't met many of these people, so I'm going over the meeting in my head, how I'm going to introduce myself, should I act shy at first? Should I walk in with a bang? should I crack jokes? And whats my natural first reaction gonna be anyway? Will they like me? Will I find them easy to talk to, or will they be kinda stand offish? What will I wear? I really don't feel like drinking, and I don't want someone to make me. Will I find the house? I hope I don't get lost. I've never been to his place before, and I don't have anyone to carpool with, but he gave me directions. I just have a scary vision of me getting lost. And I hope I have someone to talk to when I'm there. A couple coworkers that I do know said they were gonna try to make it. I just don't want to feel awkward. I really hope they come. I hope nobody asks me any embarrassing questions. I hope some loser doesn't try to put moves on me. I hope theirs no awkward silences, and that people don't think I'm weird or slow. I hope I'm not caught off guard.

But this is something that I always do before any kind of upcoming event. Even if its something as small as going to hang out at one of my friends houses, just sitting around, watching tv, or something like that. I always work myself up about it. Like I'm getting ready to give a speech in front of a thousand people.

The last party I went to, I did the same thing. When I got there it wasn't that bad, but then it ended kinda miserably. I do think that most of the time, once I get there, I'm surprisingly fine. I don't know whats wrong with me. I wasn't like this in the past. I just started getting this way these last 2 to 3 years. I'm 20 now. Maybe its because I don't really know these people? I don't know. But then why do I work myself up to be around even the ones I do know? (I'm sorry its so long. I'm kinda venting here. I'm really worried about this.)