Seconded. It's pretty wild how much a cold shower affects you physically. The only comparable things is fight-or-flight stuff like your chair almost tipping backwards or the top of a lift hill on a roller coaster. You'll definitely feel awake and alive after!

I have started doing this on days I go to the gym (3x per week) and anecdotally it has positive effects on how I feel mentally and physically. (And these effects have lasted after about 6 months of this practice.)