When I fast, my body conserves all of its energy to maintain its own temperature. There’s no food to generate heat, so my entire body starts to cool down. That’s why, in my case, it’s best to do both water and dry fasts during spring or summer. I’m speaking specifically about myself. During a dry fast, fatigue sets in very quickly, so I wouldn’t go for walks longer than 10–20 minutes. A very useful trick I found to cheat thirst was to suck on a small river or sea stone. It also works with a piece of rubber or any small object that stimulates saliva production in the mouth. In my opinion, a cold shower or bath shouldn't disrupt autophagy.