For me the first 3 days of my 21 days on water were probably the most difficult. I was mostly suffering from headaches, weakness and some nausea, but no vomiting or diarrhea. Day four however was the best of all the 21 days according to my fasting diary. I felt a surge of energy like you did and started to do too many things and thought how great my fast was going until ... I crashed and just felt like staying in bed. I felt better and worse on and off but always a little weak and sometimes dizzy until day 21.
It also depends on how toxic the body is to begin with. I read somewhere, the worse are the symptoms the more intense is the detox. You are lucky if you don't have to go to work and socialize with people. I had to go to work for the first three days of my fast and it drained a lot of my energy. I am planning to start my fast tomorrow.