He was concerned that his family wouldn't accept him upon his return from treatment. He worried that he might not be able to find a job once he graduated. He wasn't sure that his wife would accept him upon his return home. And so on.
It was always something, usually something small that was driving him to distraction. And foolishly, I would listen to his concerns until he got them all out and then give him some suggestions of what he could do to solve his problems of the day.
Then I decided to try an experiment. The next time he came to my office I asked him if he really wanted a solution to his problems. He said he did so I gave him an assignment. I told him that he would have a rule about worrying.
It was that he had couldn't worry until a certain hour of the day - which he would choose. The rule was that he couldn't worry at any other time of day until the hour that he had picked. Once that hour came he would go to his room or some other quiet place and begin to worry. And that was all that he could do. He couldn't make phone calls. He couldn't watch television. All he could do is worry, to immerse himself in his problems.
And surprisingly it worked. Once he began to worry on a certain schedule he came to realize that he did had some control over his thinking, that it didn't have to control him every minute of the day. And soon he came to realize that most of what he was worried about were small things that were of little significance or larger things that he had little or no power over.
If you face his issue, it might also work for you. It's free to try.