Yeah, I've fasted. I did the crazy sounding 'lemon juice/maple syrup/cayenne pepper' fast. I used 'gourmet hippie' maple syrup -- the same brand Beyonce used to drop sizes for her role in Dream Girls -- thus blurring the line between 'fast' and 'eating disorder'. Hey, at least I acknowledge it. Fasts are a culturally ok way for celebrites and their emulants (yes that's a word - I made it up) to basically not eat for extended periods of time.
I've done the lemonade fast for 15 days and a straight up fast with only water and occasional juice for 10 days.
The first time I felt very energized, stayed very active with yoga and rock climbing and an active social calendar. Actually, I had to sneak in chai tea (caffeine is a no no durnig fasts) and vegan cookies in the last few days to help me keep up with all the activity. And I drank A LOT of fluids.
Second time round, didn't drink enough fluids and I was so tired I literally slept 12 hours straight and up to 16 hours total a day. I was exhausted. The first time, I didn't lose weight (nor did I intend to, I wanted to see what 'detox' was), but my skin cleared up beautifully. The second time, I dropped 10 pounds on the scale and my skin looked the same and I remained sluggish for a while. I really did not fast right the 2nd time.
Did I FEEL better?
When you do it right, you feel very light and energized and clear headed. Proper fasting is attributed to many miraculous effects including lowering your blood sugar levels to non-diabetic levels, curing phantom pains, helping with allergies and depression, etc.
I do buy into the detox thing with a grain of salt, though many experts will tell you detoxing is a myth, and that in fact your body is meant to live and even thrive with all kinds of pathogens, germs, and junk in your system and or that eating the proper kinds of foods is what detoxes you and fasting is too jarring on the body. People who believe modern living and foods are 'toxic' and that the human body is based on a prehistoric blueprint will tell you your body DOES need a break from all this modern junk.
When done right, fasting does NOT make you feel hungry (except late at night

), after 2 or 3 days you lose those sensations of hunger.
Every time you do it, you learn new things about yourself, your relationship to food, your reaction to food, you becom strangely aware of things, you lose and gain allergies.
I could get truly hippie dippie here but I'll stop. Unless you want more hippie dippie perspectives on it.