Hello! I am quite new to this website, so a big hello to you all!!

I am 18 years old and a senior in high school with experience in 1-3 day Water Fasts but never had the chance to go any higher due to gym class, and forced eating through my parents. I want to get this Water Fast done for detoxification purposes, fat loss, my temporary "cure-all" for slightly-less than major depression, and simply personal excellence. It's difficult enough to have to deal with screaming from my parents due to them wondering why I'm not eating when they make something (I'm not going to explain to them what I'm doing, as they do not care), but what's even more of a buzz kill is gym class. I have no way around gym class, and I get a low grade if I happen to not physically participate. There's nothing wrong with me physically therefore I have no excuse to not participate. I have done my research, and it seems like moderate exercise is alright for the first 3 days, but even that in itself is a bit detrimental. I want to do a 20 day water fast, and if I'm destined to lose more muscle than I'm supposed to on this fast, then I can really only do these short 1-3 fasts. Is there any way around having to exercise during gym class and not lose muscle? Or do I simply just not do these long fasts? Thanks.