My Partner Is Stressed and Wont Admit It

My partner Sean is a head of management at our authority, we do not work together, he works long hours although loves his job but I fear he is getting obsessed. What I have noticed recently when we have sex he is getting these terrible headaches after he ejaculates and sometimes they carry on for some time, almost like a migrane. We have a healthy sex life and although he works long hours he still has the high sex drive that he has always had. These headaches are really getting him down, I think it is blood pressure but he wont have it and he wont go and see a doctor. Could I be right to think that it would be due to the stresses at work, blood pressure etc that is causing these bad heads. Its awful to see him in such pain, it worries me so much but when I speak to him about it he gets ratty and we nearly argue.

How can I get the daft muppet to seek medical advice without sounding like a nag.

Thank you in advance.

Princess xx