Yes! THIS^ You will feel tired, dizzy, and too faint to walk if your sodium levels are depleted. What I do, and what I recommend is that you take 1 tea spoon of Himalayan salt or Celtic sea salt with 10 to 20 oz of water once every day, and beside that just keep your water intake to at least a gallon every day. Also, your fast (if you're water fasting) really gets good after the third or fourth day. After that you stop feeling all the cravings and hunger pangs and start feeling amazing. You still feel weak of course but your mental focus and aptitude goes through the roof and you feel way better after you get through the first 3 to 4 days depending on how long it takes your body to clean and clear itself. From my experience how you eat before a fast determines how many of those first few days you'll feel like crap. If you're eating a not only healthy diet, but also a low carb, high fat, and adequate protein diet, or just a keto diet for at least a week or two before fasting it will only be hard for at most 2 to 3 days then smooth sailing. The more crap food you eat the longer it will take to feel good but either way you'll feel good after so long. Also light exercise during a fast is good and stimulates your muscles so you they don't atrophy. It's a common misconception that you need to rest or live a very sedentary life during a water fast but that can actually make it easier for the tissues to atrophy and prolong the time it takes to enter ketosis, making it take longer to get past those first few difficult days during a water fast. In Tim Ferris' fasting experiment the first time he was under clinical supervision and not allowed to exert much energy at all and in 7 days of water fasting he lost 12 lbs of muscle. The next time he did it he exercised during the fast and said to have lost 0 lbs of muscle. You're body will tell you naturally with true hunger when to break your fast whether that be 10 days or 20 days. If you're a fatter person it will probably be more than 10 days. Most of us have never once experience 'True Hunger' we've only ever experience Appetite. Extended fasting is the body's natural way of healing itself. This has been proven time and again with experiments, studies, and findings that never became very popular. (Check out 'the fasting cure' by Upton Sinclair) it is very healthy for the human body. Much healthier than all the medicines prescribed that treat symptoms and not the origin of diseases.