My girlfriend says she feels tired after masturbating. Is it true?

This is pretty common. During arousal, people’s hearts begin to beat faster and their blood pressure rises. After a certain amount of stimulation, people may experience orgasm — the peak of sexual arousal when all the muscles that were tightened during sexual arousal relax, causing a very pleasurable feeling that may involve the whole body.

During orgasm, painkilling chemicals called endorphins are released into the bloodstream, causing intense pleasure and relaxation. Some people become very sleepy after having an orgasm.