Hello and welcome!
What you describe sounds a lot like panic attacks to me. The rush that you describe is most likely adrenaline, followed by a feeling of fear, which releases more adrenaline, and continues a cycle...which is why you say you can experience it many times in a row.
Anxiety and attacks can come out of nowhere...and often you are not even aware of feeling stressed. Stress is accumulative, and we often deal and get used to a certain amount as more and more is piled on, yet we feel normal. My first attack happened when I was not feeling stressed, and in fact I thought that I was just getting decked with a sudden onset of the flu.
Since you have had all of your medical tests come back as being healthy (yeah!) it is now probably a good time to concentrate on treating the anxiety.
It is good that you are feeling better with the help of your Rx...but a med can only help so much. Is there a reason why you do not want to do the therapy? An offer of referral is quite a good thing, and one that I would urge you to think about!
I have been relieved of my daily panic attacks due to therapy and the support that I have found here.:) It could be the best investment that you could make for yourself...and one that you may want to take advantage of.
Either way, keep posting here with us. It is great talking with others who understand, and we are here to listen and care.
Talk to you 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