Every reversible reaction has an energy change in both directions. If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. An exothermic reaction releases energy to the surroundings and an endothermic reaction takes energy in.
The same amount of energy is transferred in each case. For example, if the forward reaction releases 50 kJ, the reverse reaction takes in 50 kJ. The energy is not lost or made, it is just released in one direction and absorbed in the other.
Hydrated copper sulfate gives a good example. Heating the blue solid to drive off water is endothermic, because energy is taken in. Adding water to white anhydrous copper sulfate is the reverse reaction, so it is exothermic and the mixture gets warm. Thermal decomposition of ammonium chloride is endothermic in the same way, so the reverse reaction, where ammonia and hydrogen chloride combine, is exothermic.