My GP suspects I have carotid sinus hypersensitivity, which I understand can be a complication of MG. I have had a lot of cardiac investigations and the most recent 24hr ECG showed a very wide ranging heart beat (38-186). I have had times when my blood pressure has shot up to 199/169 just while I was lying down. It was very scary feeling and I have no adequate explanation for what that was. I get palpitations lying flat and if I sit without my feet raised, which I think must be to do with the CSH. My only other thought is that obviously if you are having breathing problems the BP will rise to compensate. Hope this helps!