In shower i masturbated and i have my period, then a lot of blood came out then i blacked out. all i ate earlier was toast and tea? what could this be?

Masterbation & blood: Masterbation with orgasm causes lots of changes in your neurovascular system, a fancy way of saying that you could pass out in some circumstances. The heat of the shower, which dilates blood vessels in your skin, leaves less blood available to the brain. Low glucose from lack of eating also can cause blackout. Your bleeding is most likely just a coincidence, not caused by the sexual experience.