I think there might be a genetic link. my (maternal) aunt and i both have pretty severe postural hypotension (fainting occasionally).?

You are correct: A genetic defect resulting in low aldosterone could be found in genetically related people. Low aldosterone results in low sodium, and low sodium results in low volume, and low volume results in low blood pressure. Standing will result in less than needed blood pressure to keep the brain alert.

Yes: Pots (postural orthostatic tachycardia syndrome) has familial links. Aldosterone might be direct genetic link or secondary effect of a more primary disorder with genetic relationships. Persons with eds (ehlers-danlos syndrome), a variety of joint hypermobility syndrome (jhs), have greater incidence of pots. Theory of autonomic dysregulation is a convincing physiological mechanism to explain pots.