Welcome to Health Care Magic
You sound intelligent indeed - you have excluded the possibility of Anxiety
, as a cause for the symptoms.
It could be an imbalance of Autonomic Nervous System? / Bouts of secretion of adrenaline
as in Pheochromocytoma? - Did you check your blood pressure and heart rate?
The best option will be to see an Internist. A physical examination is a must - especially, during an attack, if possible?! Some basic lab works may be needed.
It may not be easy to diagnose - as you have no other symptom... Time and tests may shed some light.
Wishing speedy recovery