Anxiety is causing you to be super sensitive to any sense of dizziness and magnifying it. This process is similar to PTSD flashbacks.

Can we rule out PCS? I say yes, A 99% chance it has nothing to do with PCS. Even if it did, it would not change anything.

Vestibular therapy could cause a placebo effect or it could just show that your dizziness is within the range of normal.

SSRIs and benzos (valium) do nothing to reduce the dizziness, head aches, etc. of PCS from a curative perspective. They do help the mind stop focusing on symptoms and making those symptoms worse due to that focus.

Many with PCS have achieved great improvement with SSRIs because it allows them to forget these memorized symptoms and start a return to normal thoughts and life. It helps to break the cycle so one can move forward.

The acute symptoms of a TIA only last minutes to hours but some subtle symptoms can remain for longer periods. It took my wife a few weeks to get free of the leaning to the left feeling. And, it only takes minutes to hours for the anxious brain to memorize and become sensitive to a symptom.

Don't discount vision issues. Double vision is not the only manifestation of vision that causes problems. A behavioral optometrist can do a thorough assessment. https://nora.cc/healthcare-locator.html Nystagmus, convergence insufficiency and other issues can change the way the brain combines vision with balance. But, it sounds like you have already had a lot of testing in that area.

If you were to just accept your dizziness as a minor inconvenience and your new normal and move on, I bet in a few months, you will not be noticing any dizziness like you do today.