The energy that was hidden in the false vacuum is…

““The energy that was hidden in the false vacuum is liberated in the course of this phase transition of the universe into the real vacuum; it now becomes normal energy, just like the thermal energy liberated in the process of crystallization of ice in water. The Higgs field takes the place of the ice crystals as the physical vacuum develops in the inflationary model. The energy generated in the inflationary process, which originates in the false vacuum ground state, manifests itself as motion energy in the Higgs field. We might say that it makes the Higgs field shiver. It then produces radiation and massive particles that move about randomly. In this thermalization process, it increases the temperature of the universe; it spreads evenly throughout all space. Inflation ends some 10^-33 after its own Big (or Small!) Bang in the same state the universe would have reached in the hot Big Bang model without inflation. This coincidence is at the basis of our model's success. We believe we can understand all further developments in terms of various theories, some of which are quite speculative, but none of which clash with the inflationary model. The success of the inflationary scenario when compared with that of the hot Big Bang is its implied explanation of the properties of the universe after t = 10^-33 seconds; these properties have to be entered into the hot Big Bang model as unexplained initial conditions.””

— Henning Genz