This could be way off base, this is just a hypothesis. Maybe because you are focusing soully on you when you masturbate, you are more aware of the anxiety symptoms that you are experiencing? Or they seem stronger because when you are having sex, you are also focused on your wife. I don't know? Just a thought. (I tend to notice my heart range change/it beats way harder than I would normally notice when I am alone.)

Don't know if that helps or not?