It is what I call 'Performance Anxiety'.

It's not enough to have gotten the job but the obsession and need one has to prove they are good enough to keep it.

I am guessing this weighs heavily on your mind even when you are not at work. Perhaps you are even becoming obsessed about it.

Look around you and consider your place in the team. Consider there is no need to be the best of it. Consider now that other people have done this successfully; there is no reason why you can't too.

Now the hard part is to leave that worry of performance at the workplace. Is it possible to even take a longer route home? That would allow more time for you to unwind I think and get home with a clearer mind that has left some of the worries behind you.