Stress can do some pretty amazing things to the body and mind. I had a similar experience once years ago. This was even before I had been diagnosed with an anxiety disorder. I was working quite alot, and prettty stressed compared to normal. I had dropped my daughter off at my mom's on a particularly rushed morning, before dashing off the work. I hurriedly walked her up to the house, got her inside, said goodbye to her and my mom, and took off. Well, all the way to work, I was plagued with the thought that she had not made it into the house, and was still in the driveway! Ridiculous I know since I had walked her in myself, but the thought remained. I realized that I was over-stressed and this was causing my thoughts to be warped, but it was still disturbing!
Your example is not that extreme...it may seem that way to you, since you have never before experienced anything like it, but rest assured, it is certainly just stress overload. The mind and/or body will focus on something when it is pushed beyond the normal limits of anxiety. The 'normal limits' and resulting symptoms are different for each individual. Just as treatment and recovery will differ for everyone.
Talk to your therapist (or if he/she is unfamiliar with this type of symptom as your 1st posts might suggest...ask for a referral) about treatment. If you looked up the site that I put in my last post and it seems to apply to you, then inquire about treatment for OCD, GAD, or a combination thereof. There is help in the form of medication, therapy, or both.
Good luck, and I hope that you get the answers that you need soon.
S.C.