Thanks for all your responses! Ok I will keep my showers short from now. Its probably either due to low blood pressure or chlorine/fluoride. I think its the former, but not sure. I am leaning this way because the effect is immediate and is reduced if I finish off with a cold shower so perhaps the blood vessels constrict back to their normal size. If it would be a sudden influx of fluoride, then you would think the tiredness would last for more than a couple of hours.
I swear the hot water feels much better than it did when I was pre AF several years back. I think its because of my chronic low body temperature but at the same time it stresses the adrenals/body further if done too long.
I'll also make sure to have more sodium in general. I think Candida also has made me colder than I am supposed to be. Working on that.