Do it first thing. As soon as you get up. Don’t torture yourself with postponement. And don’t muck around with hot-to-cold transitions, temperature tweakings, etc. Fling wide the plastic curtain, crank the tap to its coldest, take a breath, and step right in. Not grimly or penitentially, but with slapstick defiance: Holy Mother of God! Cowabunga! Here I go! (If it’s too early in the day for slapstick defiance, try a head-shake of weary amazement.)
The water hits, and biology asserts itself. You are not a tired balloon of cerebral activity; you are a body, and you are being challenged. You gulp air; your pulse thumps. Your brain, meanwhile, your lovely, furry old brain, goes glacier-blue with shock. Thought is abolished. Personality is abolished. You’re a nameless mammal under a ravening jet of cold water. It’s a kind of accelerated mindfulness, really: In two seconds, you’re at the sweet spot between nonentity and total presence. It’s the cold behind the cold; the beautiful, immobile zero; a flame of numbness bending you to its will. Also—this is important—you can still lather up in a cold shower, and get all your washing done: hair, body, everything.
Then you get out, and you’re different. Things have happened to your neurotransmitters that may be associated, say the scientists, with elevated mood and increased alertness. You’re wide awake, at any rate. Your epidermis is cool and seal-like. Your nervous system is jangling—but melodically, like tiny bells. And from the kitchen, you can hear the kettle starting to whistle.