A patient has experienced a low, hopeless mood every day for the past four months that has not lifted regardless of positive events, alongside sleep disturbance and loss of interest in previously enjoyed activities; her facial expressions and manner of showing emotion remain entirely normal throughout. What level of disturbed emotion does this represent?

This is a morbid disorder of emotion: a sustained, pathological disturbance of the underlying mood state itself, persisting regardless of circumstances and representing an illness in its own right, here established depressive illness, exactly as described. It is not a morbid expression of emotion, since a morbid disorder of emotion differs from a morbid expression of emotion, which concerns disturbance in the outward display of feeling rather than in the underlying mood state itself — here her outward display of emotion is explicitly normal, it is the underlying mood state that is disturbed. It is not an abnormal emotional reaction, since a morbid disorder of emotion differs from an abnormal emotional reaction by its sustained, less clearly reactive nature and its greater severity and functional impact — here the mood has not lifted regardless of positive events, unlike a reaction that would track circumstances. And it is not reactivity of mood, which is heightened responsiveness to circumstances, the opposite of this sustained, circumstance-independent low mood.