See a doctor. Have never heard of this happening but doesn`t mean it exists. If this feeling occurs every time u masterbate, you should have concerns. If may be caused by the pressure & tension build up just before release. Even if you`re masterbating several times a day, you should be ok. If you have the ability, have an MRI to see if all your blood is flowing thru your brain as it should. This may pass but if not, see that doctor as soon as u can.