Hello! Welcome and thank you for asking on HCM! I understand your concern and would explain that your symptoms may be related to a low blood pressure or a metabolic disorder (thyroid dysfunction, adrenal dysfunction, chronic anemia,etc.). The fact that this occurs only in a certain position or a certain physical activity is indicative that it is not a serious medical condition. It doesn t seem to be related to any cardiac disorders (based on the symptomatology). Have you measured your blood pressure during these episodes? Orthostatic hypotension, could also explain this clinical scenario. I recommend consulting with a GP for a careful physical examination, a resting ECG, a chest x ray and some blood lab tests: - complete blood count - kidney and liver function tests - thyroid hormone levels - cortisol plasma levels - fasting glucose - blood electrolytes, etc. A head up tilt tests is needed to rule in/out a possible orthostatic hypotension. Meanwhile I recommend performing a lot of physical activity (walking, aerobics, sports), to help you maintain a good physical performance and prevent any possible similar episodes. Hope to have been helpful! Best wishes, Dr. Iliri