in my experience, cold showers can work wonders, but it depends on your current physical and metabolic state. if you're in a lethargic state, then it's probably not going to help (and if it feels painful, then that's not a good sign). but if you're in an agitated state (which is the kind of mood disturbance i usually have. i guess it's like a milder version of bipolar mixed episodes), then it might help, especially against insomnia, because it wakes you up and calms you down at the same time. and at least to me a cold shower actually feels great after vigorous exercise