Hi M,
Too hot for us too! S struggles to regulate his body temperature and can over heat even when others think its a cool day.
Water pistols sound fun. Hopefully the kids will burn of plenty of energy and sleep well tonight, even if its another hot night.
I don't have experience of FND or ME but I think heat lowers the ability to tolerate pain. I had one hip operation during a heatwave (hospitals are too hot even when it's not a heatwave and their windows rarely open more than a chink) definitely pain felt worse when too hot.
Melly1