Every once in a while when I jump in the shower, warm water will feel like hot water - the back of my hand can feel it as warm but the palms of my hands feel like they're sunburned, and when that happens, I know my scalp will burn so I have to turn the water almost on cool - actually drinking warm liquids will feel very hot to my tongue.

But all of this only happens like maybe once per week

Sometimes our nerves do weird things that we don't entirely understand. Like the experiment you can do in your home. You take a glass of ice cold water ( lots of ice cubes in it. And one with hot water ( almost as hot as you can stand ). Then put each hand a few fingers in each glass. Then after a minute switch them. The ice cold will feel hot and vice versa. That may be what your experiencing with the shower routine. Cold can still feel cold even when its hot.