Why does after orgasming, it makes me sleepy and sometimes even causes me to sleep? thank you! m18?

During orgasm, the brain releases many hormones and neurochemicals, mainly oxytocin, dopamine, and serotonin. These "feel good" chemicals have a profound effect and result in the pleasure and sleepiness that you feel. ref: https://www.sciencealert.com/here-s-what-happens-to-your-brain-when-you-orgasm

It is a normal reaction for the body to calm down after intense activity. Nothing to worry about