Extreme weight loss is always a bad idea.  Many people use laxatives, diuretics, and other harmful chemicals in general to achieve these results.  So that’s obviously related to it being a bad idea.  But even if you don’t, the majority of what you are losing is going to be water weight, it’s a simple fact.  Moreover, it’s going to take away things you actually need.  It can easily be abused, and frankly skipping meals can be defined easily as extreme weight loss methods to say the least.  It is dangerous to your health and can actually lead to serious heart problems among other things. 

In extremely overweight people, other people in general often are jealous, want to achieve the same overnight type results, etc and so on.  It’s appealing going from good to bad overnight.  But it’s not as good as you think, it’s really not.  While skinny may seem healthy, in this case it’s definitely not always so.  Many heavy adults actually report dieting from a young age paradoxically speaking.  But it’s far more sustainable if you lose weight at a slower rate.  It may seem unappealing during that time to see smaller results.  But when you are staying thin and not having to diet again and again, it will be far better.  And when you’re not in the hospital or experiencing other rather extreme side effects, well it will definitely be more appealing then.