I have also been doing cold showers, for a while now. It's crazy.
Right now in the middle of winter, running my head under the shower for 30 seconds causes light-headedness.
Isn't it awesome! It makes the rest of the day easier. I find putting the rest of the body in invigorating.
It has the same motivational pattern as exercising and many other activities: Long before you do it you think "No problem, however hard it seems, I'll will myself to do it and my willpower will make it easy." Just before you do it your mind goes crazy with excuses not to do it, to do it tomorrow, that not doing it is no big deal, and so on. Doing it is uncomfortable. At first you think "Holy shit, am I actually doing this?!? This is crazy!!". When you're almost done you think "That wasn't nearly as hard as I thought. The anticipation was worse than the experience." Then after you do it, the discomfort disappears immediately and you feel great for doing it.
How many great parts of life do we lose in this part: "Just before you do it your mind goes crazy with excuses not to do it, to do it tomorrow, that not doing it is no big deal, and so on. Doing it is uncomfortable."
Exercise, cold showers, meditation, SIDCHAs, and things like that develop the skill to overcome that creative avoidance.