It's definitely not healthy to lose so much weight in a short period of time. I think the maximum safe amount is like 2lbs a week. But of course you'll lose weight when clubbing because it's so hot, you're constantly moving, if you take e it's even worse. Losing weight might be a good thing for some, but not like this. Do it the old fashioned way - work out/diet. Just to be on the safe side.