When an atom emits a photon, the energy of the atom is not conserved in the same state, as the emission results in a change of energy. The energy of the emitted photon must be accounted for, indicating that the atom loses energy equal to that of the photon. The total energy of the system, including the atom and the emitted photon, remains constant before and after the emission. Thus, while the atom's energy decreases, the overall energy of the system is conserved. This illustrates the principle of energy conservation in quantum processes.