Your brain may subconsciously adjust your activity as a result of dieting, but that doesn't change the fact that it is physically impossible for your body to store energy you didn't consume.
Your body will never go under such heavy energy conservation that you cannot lose weight, and it doesn't have enough control to do that anyway. At best your body can attempt to slow down your physical activity and slow down digestion for efficiency. Yes as you diet your metabolic rate will decrease, and even if it were to decrease an impossible amount like 50+% you would still be able lose weight by comsuming less energy.