Hello! Thank you for asking on HCM! I understand your concern, and would explain that your low pulse rate is not related to eating. The light headedness and tachycardia when you stand seem to be related to an orthostatic hypotension or a postural tachycardia syndrome. Are you taking any medications lately? (These symptoms may be related to drug adverse effects too.) I recommend consulting with your attending physician for a careful physical examination, a resting ECG, a chest x ray, a head up tilt test (to confirm the above diagnosis) and some blood lab tests: - complete blood count - PCR, sedimentation rate - thyroid hormone levels - blood electrolytes - fasting glucose - immunological tests (anti ganglionary antibodies), in case of confirmation of postural tachycardia by head up tilt test. Regarding your period irregularity, I recommend consulting with your gynecologist for a physical examination, an ultrasound and sex hormone blood levels (to exclude possible hormonal imbalance). Hope to have been helpful! Best regards, Dr. Iliri