Chief among those laws is the conservation of energy, which rightly says “energy can neither be created nor destroyed”. But the conservation of energy operates on a frame-by-frame basis, not between frames. That is to say, the amount of energy in a system changes (only) when you change reference frames. In the hazy days of Newtonian physics we knew all about conservation of momentum and independently the conservation of energy. The point is: just like velocity, energy is subjective and changes in very much the same way that the direction of velocity changes when you turn your head.