I am going to take a shower.
Standing in the shower room, looking at the shower valve, there is a voice telling me
You’ve got to take a cold shower
I couldn’t resist, so I followed. Some people may put a bit of cold water on the legs and/or some other body parts to get prepared. But I find that more stressful and unbearable. So I just turn on the tap to the end, the cold water rushes out with maximum speed and volume from the shower head, it hits my head, then the rest of my body. It’s like suddenly jumping into a cold lake, or being crushed by a water cannon.
When the cold water flows through my body, especially my back (I guess it’s because there is less fat and more nerves), whatever I am thinking about gets purged from the brain. The signals coming from all my body blocks the normal processing ability of the brain. I want to scream, but what’s the point of screaming? Instead, I start to show a poker face like I feel nothing. Then I laugh.
After twenty five seconds, my body gets used to the cold water, and the brain is able to allocate more space for normal thinking. The cold shower feels like a warm shower now. The essence of taking a cold shower is the first twenty five seconds.
There is a paper Adapted cold shower as a potential treatment for depression, which is also interesting.