CNS causes include HEAD:
Hypoxia/Hypoglycemia
Epilepsy
Anxiety
Dysfunctional brain stem (basivertebral TIA)
Cardiac causes are HEART:
Heart attack
Embolism (PE)
Aortic obstruction (IHSS, AS or myxoma)
Rhythm disturbance, ventricular
Tachycardia
Vascular causes are VESSELS:
Vasovagal
Ectopic (reminds one of hypovolemia)
Situational
Subclavian steal
ENT (glossopharyngeal neuralgia)
Low systemic vascular resistance (Addison's, diabetic vascular neuropathy)
Sensitive carotid sinus

 Mnemonic:
HEAD HEART VESSELS