Here's my cold-shower report:
I started taking cold showers on August 16 (about five weeks ago). I'm thin and have always disliked cold.
On the first day, I hyperventilated for the first minute or so. I was amazed that I had no power to control my breathing. I'd read that people drown not because they're bad swimmers but because cold shock triggers involuntary deep inhalation, and this brings water into the lungs. Well, now I *know* what that's about!
Once I was breathing normally, I washed my hair as quickly as possible and got out of there. I felt pretty invigorated for the next hour or so. I hoped that this was an "opponent process", and that future showers would make this invigoration period last progressively longer.
For the first few days, I kept my showers very short. Then I noticed that after a few minutes, the water felt *almost* warm. Hooray, thermogenesis! After that, I've usually gone about ten minutes, feeling no need to hurry.
Somewhat disappointingly, after those first couple showers, the invigoration after the shower has lasted for much less time, not more. I've even fallen asleep half an hour after the shower.
Various small things:
* I've only shivered on one day, about a week after starting. (I'm thin and normally shiver pretty easily.)
* While I haven't hyperventilated since the first day, I've found myself deep-breathing uncontrollably for the first 30 seconds or so each day.
* I haven't successfully measured the water temperature. (I tried putting a cooking thermometer into a cup of water from the shower, but I ended up convinced only that the thermometer was seriously miscalibrated.) I strongly suspect that it's warmer than the recommended 50ºF or 59ºF. The shower control mixes warm and cold water, and it's summer in the American Midwest.
* On a couple days, I went to the kitchen sink to pour some cold water to drink, put my hand under the faucet to sense when the water was cold enough, and found that it didn't feel cold to my hand even after I let it run a while. Without a thermometer, it's hard to say right now if that's because the water actually was warmer or my sensation of cold was shifted to lower temperatures.
* Even though I know full well that the water will feel fine after a couple minutes, I still feel a bodily revulsion before getting into the shower, which I have to overcome by willpower each time.