Not to scare you but- The first time I did this diet I was with my friends and I drank my two litres during the day. Later we decided to go out and I was sitting in the pub drinking water. I think I drank another 3 litres so that's 5 litres in total. What happened next was really weird. I felt like I needed to go to the toilet really bad so I pushed through the crowded nightclub to get to the toilets but by the time I got there I decided I was ok and a bit of fresh air might be better for me. As I was leaving the club I stumbled. The bouncer thinking I was drunk threw me out. I passed out on the street outside the nightclub. I was so lucky my cousin - who knew I was on the diet found me. He threw me into his car and started to drive me to the hospital. My speech was slurred and I was very uncoordinated. I got him to stop the car and I got sick. I was there for about ten minutes vomiting pure clear water. Then I went to sit back up and I was fine. No slurred speech, no light headedness, my coordination was back. Everyone's body is different. I found that drinking 4 litres of water is not a good idea for me on a daily basis. I drink 3 and I am very carefully not to drink any after 6pm - so I get a good night's sleep. Be sure to keep track of your in take. Too much water is very dangerous. I know.