Hope your first day on the job went well. By now, you're pretty well into it. Just wanted to send a note to say that I know what you're going through. I'm starting a new job in a couple of weeks, and already I'm plagued with pangs of anxiety and negative thinking (i.e. what if my new boss if mean, what if they make me work until all hours of the night, what if I can't do the job, etc.).
Victoria had some really good advice. Simple as it seems, it never occurred to me to think of the positives.