You should be perfectly fine (as long as you don't have any pre-existing health problems) and most of the folks that'll tell you you'll die or whatever have no idea what the fukk they're talking about. Fasting can actually be one of the healthiest things you can do for yourself.
HOWEVER, and it's a big however, why are you looking to fast for 10-14 days in the first place? If this is just some emotional crash diet attempt, you should probably chill. Try a 2 or 3 day diet max and look into changing your exercise and eating habits in a more sustainable way. Whatever you lose will come right back once you go back to eating regular again.
Having said all that, if you choose to go the fasting route anyway I'd say:
- Drink at least a half a gallon of water daily, but don't go overboard, keep it to a gallon max
- You're gonna need to supplement with sodium and magnesium to keep yourself from feeling too off. Get Himalayan Pink Salt and take about 1 teaspoon a day for your sodium/electrolyte intake, you can just put a couple crystals under your tongue throughout the day. Magnesium in powder form is the best form to take so you won't break your fast, check bulk supplements brand on amazon, or natural calm magnesium. The Magnesium helps alot with your sleep, without it my sleep tends to be all fukked up on a fast
- Eating or drinking anything besides water and salt means it's not a fast. Lemon juice diets are not fasting, having a little bone broth is not fasting, having coconut oil with coffee is not fasting. All those things contain calories and will break your fast. Water, salt, a little magnesium powder, that's it.
- don't lift weights or do any kind of strenuous exercise, just rest and let your body do it's thing
- and if you feel really bad at any point during the fast, like very lightheaded or seriously ill, be smart and just eat something (start light, a small piece of fruit or something like that)
Good luck, and probably do some of your own research on extended fasts as well before jumping in, it helps to get an idea what you're getting into