My first and second time experience with three day fast

For both attempts I wanted to do a three day fast. Ended stopping both after 48 hours.

The first attempt, I drank water and added a little bit of salt only. Sometime midway, my hands started feeling numb. So did my legs. I didn’t feel safe continuing, so I stopped on the second day. Had a light meal and slowly got back to eating. I figured I wasn’t taking enough electrolytes.

For the second attempt, I took LMNT with water. I figured the experience would be better because I was adding other electrolytes that I didn’t do the first time and higher quantity as well. Same result during the second day. Not only that, but a few days later, even though I wasn’t fasting anymore, my heart rate spiked to the 140 range just from walking a little bit and got extremely out of breath.

Any advice on why this happened? Did I not take in enough LMNT? Should I have taken something else as well? I’m not much of a coffee drinker so didn’t drink any during the fast. Figured the caffeine might do more harm than good since it’s not something I drink on a regular basis.

What can cause numbing of the limbs?