I'm sorry to hear you aren't feeling well. Others on this forum will be able to address whether or not this would be considered a "relapse". From my limited experience, I would not say "relapse". I would say you are simply still healing.

You really, really, really need to get a copy of "Brainlash" by Gail Denton. She has printed a graphic in there that describes her theory of how the brain hits plateaus and peaks during healing.

She also has a lot of great information about disinhibition. She also had a whiplash injury. Not to be overly dramatic, but NancyS on this forum suggested the book and it literally changed the way we have viewed and treated my daughter's injury. It's a relatively short, easy to read book. I think it's $13 on Amazon.

The fuzzy thinking symptom is so darn scary. I find it easier to deal with if you keep equating the brain injury to any other type of injury. If you had hurt your knee five months ago and were still struggling once in awhile to walk under stress you wouldn't freak out...you would realize you are still healing. Try to be kind to yourself in this respect.