Hello, This is just a normal response of the body when your autonomic response is stimulated. Your brain needs oxygen to function hence the vessels in your neck responds by contracting. in your case, laughing so hard portends losing oxygen supply when needed and failure of your vessels to respond fast will lead your blood not reaching its destination on a given time. The effect would be dizziness. Headaches comes from the vasodilation of your brain vessels which is in turn a response to the poor oxygenation. This is just normal and nothing to worry about. Its a response. I cannot advice you not to laugh so hard because there is nothing wrong about it, but what you are feeling is just basically normal response of the body. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Palisoc, Neurologist, Surgical