Start job again tomorrow after anxiety how do I cope?

I work from home taking inbound calls. The job is actually quite easy and there are always people on the other end of the phone to help if I need it. I do not want to lose this job. I am starting back tomorrow after having 2 months off due to anxiety. I see a psychiatrist who said only to do a little work. I am petrified about tomorrow. I know this is totally stupid as I am only working for 30 minutes but I probably wont sleep tonight due to the worry. I know I can do this job easily but why do I keep getting such anxiety over nothing. I have not worked for 2 years before this job and feel totally useless and hopeless. I dont want to lose this job and I want to be able to do it, but I just cant see it, any ideas what can get me through. I know people want work and I have it laid out for me, but that doesnt help