For me, the best way of dealing with anxiety like this is just not to think about it. Just don't think about going back to work at all, put it out of your mind.
I've never been successful in trying to think my way out of anxiety. The more I think about an upcoming anxiety-causing event, the more anxious I get, even if I'm trying to come up with strategies for dealing with it or telling myself it won't be that bad.
Instead I picture how I would think about going back to work if I were a very relaxed, non-anxious person, and the answer is, it wouldn't really be on my mind at all. I would be doing and thinking about other things until the time came to go back, and then I would just go without thinking about it much at all.
I hope that makes sense. It can be difficult to put an upcoming anxiety-inducing event out of your mind, but I find it works better than anything else.
Of course, if taking medication is an option for you, you could go that route. Paxil has reduced my anxiety a lot, but it doesn't work for everybody.