11 Day Fast Felt Messed Me Up: Why?

Hi,

I fasted on only water 10 years ago in college. I went for 11 days. I broke the fast, and felt insanely hungry. I developed pain in the tendons in my legs so whenever I ran it would hurt, and I just all around felt like crap. I experienced extreme fatigue, lack of energy, sexually less oomph, and depression. I've spent the last 10 years getting healthier, but I just don't understand how this fasting stuff could help so many people, but there is no doubt it messed me up.

What gives? I'd like to make sense of this, because in principle I agreed with the fasting concept, but I can't come to grips with the reality that the result of that fast was not what I had hoped.

Thanks for the help,
Alex