When you lose body fluids at the same time as you are losing body fat, you are asking for trouble. All that loss can do damage to your body that you might not appreciate.
This is why a consultant or physician is helpful as you enter into your weight loss program, so that you do not make a mistake that could put your life at risk.
Your body stores up energy in the form of fat just under your layer of skin. The amount of fat you have on your body is a measure of the amount of energy you need to burn off.
You can concentrate on that as you work to lose your weight back.