Two days is the worst possible timeframe for a planed fast. Fasting means eating no food at all, and it goes like this:
Day 1: you're hungry
Day 2: you're extremely hungry, to the point where it's difficult to function.
Day 3: still hungry, but not so bad.
When going to sleep at the end of day 3, your hunger is almost gone, and by day 4, you're no longer hungry. Your body goes into ketosis mode, burning fat, no longer dependent on food. Your body detoxes itself from chemicals and impurities you've ingested over time.
From day 4 on, you'll feel the difference as your body detoxes. If part of the reason you fast is because you want to loose weight, you'll see it in the mirror by day 4, other people will notice by day 7, and you can objectively measure it if you weigh yourself on a scale. Just by breathing (O2 in, CO2 out) you loose a about a pound a day.
You'll know when it's time to break the fast when your hunger returns, or if you feel weak or light headed. Do so with a bowl of soup or a very light small meal.
If you're super thin and just want to detox, 6 days is perfect. If you want to loose weight, 10 or 14 days is good. If you've done it a few times and want to push yourself to the limit, you can go 30 or even 40 days. This is headed into breatharian territory - don't be an idiot and ignore your body when it tells you it's time to stop.
Short term fasts can be beneficial too. Eat only 1 time a day, or go a full day without eating. But fasting for 2 days is the wrong way to go - that's long enough to give you a strong hunger discomfort, but not long enough to invoke ketosis and its health benefits.