Hello ! Thank you for your question on HCM! I think you are right and the laugh and coughing may have caused a gap of oxygen perfusion to your brain. Another explication would be the abrupt raise in the intrathoracal pressure causing a vagal nerve response and other changes. The muscles of your face and neck may be contracted from hyper extension during laughing and cause headache and dizziness. So you see that there are a lot of possible explanations to this situation , but nothing serious, to be worried about. Hope to have been helpful! Best wishes! Dr. Abaz Quka