I went 5 years car free, now am in a situation with a 24 mile one way commute because of family. Now I drive 3-4 times a week and ride 1-2 times. It's been a tough transition, and hopefully not permanent, but at the end of the day I had to convince myself that it's all in my head. I found myself getting extremely frustrated and unhappy with the drive. It was definitely worsened by the lament of missing my bicycle commute and was affecting my home life and work productivity.

Now I think of what a privilege it is to ride when I can, and how fortunate I am to own a car and am able to afford to drive when needed. I set my cruise at the speed limit, enjoy my coffee, and catch up on audio books or the news when I drive. I see people do stupid things every day when I drive, but I don't let it get to me anymore. Yes I miss my bike, yes I feel better when I bike, but really it's all in my head, and I believe that being an occasional bike commuter has actually made me a better driver than when I was a full time bike commuter. Know your enemy, so to speak.

Some day I'll be car free again, but if it's not an option with your given situation, I don't think it's an excuse for mental problems.