Explain why reactivity of mood is described as an abnormal emotional reaction rather than a morbid disorder of emotion.

As an abnormal emotional reaction, reactivity of mood is ordinary emotional responsiveness taken to an excessive degree, meaning the underlying pattern, mood tracking real circumstances, is a normal human capacity that has simply become disproportionate rather than being replaced by an entirely different, sustained, illness-level disturbance of mood. This places it at the milder end of the spectrum of disordered emotion, alongside other abnormal emotional reactions, rather than among the morbid disorders of emotion, which are sustained, pathological disturbances of the underlying mood state that persist regardless of circumstances rather than remaining closely tied to them. Recognising reactivity of mood as an exaggeration of a normal capacity, rather than a distinct illness-level mood disturbance, helps place it correctly within this broader spectrum.