It is a sexual headache. I get those from time to time. It is harmless. However, mine would not last a day.

learned a new slang word from you - "fapping".

What I would do is start a spreadsheet and record each instance of masturbation, whether you had a headache (Yes/No), and if the answer is Yes, then the duration. So column A date, column B Yes/No, column C, optional, duration. After a couple of months you would see a pattern, and if you are still concerned at that time, set up an appointment with a neurologist and bring a printout of the spreadsheet with you.