Im no expert, but five days might be a long time for a first fast especially if you’re feeling weak. Im sure others with more experience will weigh in on the subject
Well, I've kind of done something similar before, although I was pretty sick at the time with something, but that was only three days. Something else I did take during was a colon cleanse powder to help move things through (don't want too much sitting in the tubes for too long I think), but honestly 5 days wasn't as difficult as I thought it would be, keep in mind the body can (supposedly) go for three weeks without food, most likely longer if you're a little bit stockier in build, but I remember I think Daniel was on a fast for three weeks, and Christ himself was on a 40 day fast...but that was no bread or water...call that another miracle because I don't think a normal person could even hope to survive that long without water.
Oh, and you're definitely right about "churches" not teaching it, closest I've heard is the whole Lent bunk where they say they'll fast mobile phone use, or something else that's ultimately a minor inconvenience at best. I remember hearing one person discuss fasting and relating it to the discussion of Mosaic law, where the fat of sacrifices was to be burned on the alter as a sweet savor to God, he thought maybe there was some link between the fat we burn when fasting and the fat that used to be burned on the altar...now do either of us know for sure? No, no idea but it's something to consider I suppose. But I haven't heard any teachings about it in church buildings, which is weird considering it's not exactly obscure or hidden in the new testament, and then there's always that verse that kept going in my head from Matthew 17:21 when Christ's disciples couldn't cast out an unclean spirit, then he told them:
"Howbeit this kind goeth not out but by prayer and fasting."
What makes me stand up and take note of this verse is that it's been removed from a lot of "modern versions". Simple math but I believe that if the modern perversions of the bible are the subtle work of the devil, then he would want to remove some of the most important parts, therefore, it can act as a guide of sorts as to what scriptures we should pay special attention to.