I'm watching a Leonard Susskind video about the Higgs Boson where he gives an example of how an electric field can change the mass of a water molecule. If you put a water molecule between two capacitor plates (so the electric field is uniform and the field lines are parallel), it will tend to align with the field because it's a dipole. The tendency to align represents a potential energy, so a 'misaligned' water molecule in the field picks up extra mass from this potential energy. In the video, he shows a diagram of two water molecules in the field, one aligned with the field, the other upside down (so the first is lower mass than the second). Then he says that the field "increases one mass, decreases the other mass". I understand the mass increase, but I'm confused about why the molecule that is already lined up with the electric field will have a mass decrease. Wouldn't this molecule keep the same mass it had before the introduction of the electric field? It seems that if it doesn't need to rotate (already aligned), then there's no extra potential energy, so it's in the same energy state as it would be without the field. at about 35:25 minutes in.