If you have had medical tests and the doctors think you are ok, my advice is to trust them. I have had the same pattern of thinking in the past and at times still do. Have you talked to anybody about this besides your doctor? Talking to a therapist (i.e. psychiatrist, psychologist, counselor, etc) is, in my opinion, the best way to understand anxiety and panic. I am a big supporter of medication combined with talk therapy, but as a combination; learning the way you think is important and the medication is a tool to help you along the way. Good luck and please keep us posted and continue using this forum.
Brain fog has no definition in medical dictionary, however, many people use that phase to explain their symptoms. Most related disorder to brain fog is depersonalization or derealization. But whatever it is, it is definitly a symptom of anxiety. Klonopin does tend to stop working after a while. But when it leaves your system then you can start using it again. In meantime, I suggest you ask your doctor about Celexa instead of Cymbalta. Also, to reduce your symptoms, try other benzos like xanax or ativan. They might or might not help but give Celexa a few weeks and then try Klonopin again.
Good Luck
And the doctors have said it is anxiety and or depression. I do not understand why the Klonopin would suddenly stop working. Now I am on Cymbalta and it does not do anything. The hazey, fog feeling is almost tangible, I need help.