hi and welcome. well type 3 ehler danlos is associated with heart conditions like mitral valve prolapse and dissections of aorta , as it affects the vascular collagen . the syptoms of POTS you mentioned are not directly related but if you have arterial rupture with loss of blood as with gastrointestinal bleeding, for example. the symptoms of chiari malformations are .... headache, esp with straining and coughing and sneezing neck pain around to the shoulders poor hand coordination visual problems , difficulty swallowing , and bladder problems but you dont have any of these. for frequent palpitations and loss of blood pressure , one can consider cardiac arrythmias... get an ecg and holter, and consult with cardiologist. chiarimalformation is not that common and its presentation is different of what you stated. thanks and take care