40° cold plunge

We take something like cocaine, a really powerful drug in our world, that will 2.5x the dopamine, so it goes up 2.5 times, peaks at 9 minutes, so it peaks really, really quickly, and then it'll begin to crash, which, if anyone has interacted with that drug, you start wanting it more and more frequently throughout the night. The cold water immersion is the only behavior they've found that can also 2.5x the dopamine. The same as what cocaine can do. Other than it peaking at 9 minutes and then crashing itself out, it rises to 2.5 hours.