Ketones are the end result of "incomplete" breakdown of fats, with the ketones being the "remnants, ash, etc." left over from this. Ketoacidosis IS dangerous in a diabetic, no question about it. Ketoacidosis however IS NOT dangerous in normal healthy humans adapting a high fat/protein, low carb diet. Acidosis simply means an increased amount of acid in the blood. Ketone bodies are acids and therefore CAUSE acidosis. There are several other chemical mechanisms by which the human body produces acidosis, and many ways in which the body compensates for ketones to maintain a normal pH balance. In normal humans adopting a ketogenic diet, the ketoacidosis will correct itself in one to two weeks, and the pH of the blood will then remain normal throughout the remainder of the diet. Changes in the water and electrolyte content of the brain are rapidly compensated for by the rest of the body. It is really that simple.
So, as you can see, it might take your body up to two weeks to adjust to the PH levels. In turn, some people do not respond well to Low PH level and they will retain water. I have talked to numerous of people that complain about water retension while others say they lost water. I think it all depends on the person.
(I'm not sure, but I think this, refering to the water retension due to low-ph, might be an alergic reaction. not all ppl. experience it) --I'll go today and look it up in the library--
I'll also echo some things that the people before me said:
Basically, when in Ketosis your body starts secreting sodium, water, and some pretty important nutrients along with it. (take multi vitamins and minerals daily along w/ Chromium picolinate) That is why people say you look harder while in Ketosis, but smaller due to the fact that there is no muscle glycogen.
Now, the problems people have with water retension while in ketosis are not that simple and sometimes hard to pinpoint, in my view. It can be either too much sodium, not enough water, not enough nutrients in the body, or you might be alergic to something you are eating.
Try to look at the list I gave beforehand and see if any of these might apply to you. If so, then correct the problem. As far as alergies go, that is for you and your doctor to decide.