Orthostatic syncope (10%) is defined as an orthostatic drop of >20mm systolic blood pressure or >10 mm diastolic blood pressure. This may be due to absolute volume depletion from dehydration or haemorrhage or to venodilatation caused by medications or autonomic insufficiency (eg as occurs in Parkinson’s Disease). It is NOT the same as reflex syncope caused by orthostatic stresses, although the clinical presentation is very similar.
Sympathetic activity is chronically impaired, so vasoconstriction can't happen. This means when you stand, the BP falls.
Syncope is one symptom, others include dizziness/ lightheadedness, pre-syncope; weakness, fatigue, lethargy;palpitations, sweating; (iv) visual disturbances (including blurring, enhanced brightness, tunnel vision); hearing disturbances (including impaired hearing, crackles, and tinnitus); and pain in the neck (occipital/paracervical and shoulder region), low back pain, or precordial pain.