Heatstroke season — non-AC ways to cope, and what happens to medical costs if you collapse?

Kansai summers get scarier every year… Running the AC nonstop is scary for the bill, but toughing it out and getting heatstroke defeats the purpose. What are your 'besides AC' tricks (cooling goods, sudare blinds, water + salt)? And if you ever need an ambulance / #7119 for heatstroke, how do medical costs work under 国保 — I'm anxious about it as a foreigner. Anyone with experience, please share.