Hi Parttime,
I am sorry you have been struggling with these symptoms.
Lara has done a great job of covering some possibilities.

I hope you have looked into the ones she has mentioned.
I would also encourage you to consider an EEG, with the type(s) of EEG to be determined by a Neurologist and/or in collaboration with a Neuropsychologist.
You may also benefit from a thorough Neuropsych evaluation. These types of evaluations can help to look at brain functioning, etc.
In addition, I am encouraging you to try some "grounding exercises."
Here's a list of simple "grounding exercises" offered by Andrew Weil. M.D.
https://www.livingwell.org.au/well-b...ing-exercises/
There are also other types of grounding exercises available on youtube and on various sites online.
You may also find a particular breathing exercise grounding, centering and it may also help you with clear thinking. I had recently posted this in a different forum. This breathing exercise is offered by Andrew Weil, M.D.
http://www.drweil.com/drw/u/VDR00112...nstration.html
You will find additional breathing exercises at various sites online.
We have started a thread of breathing exercises in the Anxiety/OCD forum.
You are welcome to join in on that thread as well. Please post any breathing exercises you'd like to share.
I hope these exercises help you out. It may take some time of regular practice. I'd encourage you to also continue your quest for an explanation for your symptoms via the testing mentioned.
I hope something helps you in a significant way.
Warmly,
DejaVu