Noise in the Shape of Writing

Here's a wierd one. Maybe someone knows the answer. Why does simply getting into my swimming pool make me super sleepy within hours? It never fails. Even if I just get in for a dip... no swimming, no underwater jumping jacks, no water fights.

Is it the chlorine? It isn't the sun cause I am in it after sundown. And it's not "cause it's after sundown... you're getting tired by then, for pete's sake" cause it's truly like night and day how much sleepier I am earlier in the evening after a dip.

I am thinking it's the chlorine.

I will test this by ingesting chlorine tablets instead of swimming.