Your problem can be either due to the anxiety or stress induced or you have arteriosclerotic vascular disease
. To rule out for vascular disease you have to do your color Doppler of the carotid arteries and if needed angiography
of the same. There are some region that this may be due to neurological deficit but you have all your scans normal, so chances are very less.
If all reports came back normal than you have to consult your psychiatrist
and have proper counselling
Try to be relax. Regular exercise and meditation can help you a lot.