Ketosis is not a usual state for the body to be in. It is a back up state when the body (the brain in particular) can no longer rely on its main energy source, glucose, sugar's most basic form.
It is not necessary or recommended for weight loss. Energy levels will be drastically reduced and your ability to sustain and recover from any activity will be compromised. Weight loss is about burning more calories than you consume in a healthful manner. Incorporation of increased activity with cardiorespiratory exercise and resistance training along with a sensible reduced calorie diet is the way to go!