Severe dizziness w/ ES is usually a sign of some type of vascular compression i.e. either internal carotid artery - which on rare occasions can lead to a stroke or internal jugular vein which keeps blood from flowing out of the brain at the rate it needs to & leads to intracranial hypertension (IH) causing pressure in the brain to be too high. Both types of compression come with other symptoms, too.
There is good information about this in this posts by Jules:
It would be a good idea to see a vascular doctor to get a dynamic angiogram of both your ICA & IJV if possible.