The coldest water you can get, no music, no sound, just feel the water and feel everything that you feel right then and there. Entertain every thought (negative and positive) and analyze it to the greatest extent that you can without writing it down, just ponder. Take a walk right after and do the exact same thing, maybe you play music but allow yourself to wander, somewhere familiar, somewhere unknown, anywhere. (Gloomy days are the best reset days imo)