Getting back to the serious ? of the OP, try drinking sports drinks now, until you are pissing often. If that does not stop the headache the next time you cum, see a doctor before cumming again. Those who had this might chime in again but it seems to me that headache with nausea and vision irregularities dictate you see a doctor. If you call a doctor's office and you are completely honest with the person scheduling your appointment, if they want you to come in right away, you know it is nothing to joke about and you should not delay. Even if it is dehydration, it could take a few days to fully recover.
Stay in touch!