you lose hair when you start eating again because it doesn't fall out at all when you're doing the diet. It's perfectly normal given the ketosis you've been through and my hair is now completely fine. It's never looked 'thin'. It was just the case that more than normal was coming out for a couple of months.
As for your kidneys, if you drink the recommended amount of water there shouldn't be any problems at all.
You get more vitamins and minerals on this diet than you would when eating normally. It's changed my life. One year on I'm healthier than ever. I can exercise properly and go running every day. My joints don't hurt any more. My eczma has gone.
So yes, there are horror stories, but if you do it properly, the rewards to your health are only positive. Surely it's got to be better than being morbidly obese?