Anecdata: ice plunges are a meta-cognitive skill. Several minutes in 45 F water results in a 12h+ boost in mood and good feelings in the limbs and skin, and 2-3 hours of heightened attention. I’m currently doing this ~4 times a week.

It’s the opposite of addiction’s dopamine cycle - a small pain the leads to a long-lasting high, rather than a drug’s small high that leaves you in its debt.