Acceptance is key. Look at the things that you know to be true first of all.
Your doctor has run tests and says there is no need for concern, as no seizure activity was present. Also the MRI showned that your brain is structurally fine.:)
If you were suffering from a stroke, you would have more than the feeling of derealization (a common anxiety symptom!)...you would be having cognitive and physical problems that would be hard to ignore.
I have had this symptom from time to time myself, and I work to ignore it as much as possible. The more you can do that, the less it is going to bother you, and go away sooner.
I hope that you get some relief from this soon!
"Courage is not the abscence of fear, it is feeling afraid and doing it anyway!"
"Worrying does not empty tomorrow of its troubles...it empties today of its strength."
Corrie Ten Boom
Panic Syndrome recovery due to CBT