Had an orgasm this morning now im totally crashed for the whole day

got no energy or stamina to do anything since. Complete ruin of day. Why is sexual excitement crashing my ability to face the rest of the day? This is a reason why i dont find sex a desirable thing like everyone tries to make out it is and if i was in a relationship i'd be useless.

All i've wanted to do is go into a darkened room to sleep all day.