Overwhelmed

So, I started a new job this past Friday.  I was really excited for it.  But after 2 days at the job, I'm kinda freaking out.  I know I probably shouldn't be, but I just feel so overwhelmed by the job.  Maybe it has to do with the fact that I started just 3 days after I had surgery for my carpal tunnel and I'm still in a lot of pain.  Maybe it has to do with the fact that I'm severely obese and not in shape at all, and the job has me on my feet for many hours at a time.  Maybe it has to do with the fact that I'm scared to have a job at all because what happens if I'm not perfect?!  I dunno, it could be a lot of things.  But I'm freaking out.  I had today off, but I'm back there tomorrow for several hours, and the rest of the week I work 7-hour days.  And I'm just scared.  It's almost like I feel as if my life is ending because I took this job.  It's not even a full time job (because I'm still looking for a full time job in my field).  Not every week is going to be full time at this position.  I know that.  But I'm still freaking out about having to go back to work tomorrow.  Maybe tomorrow I will feel a little better.  A good night's sleep should help some, right?