What subtype of depression is characterized by mood reactivity, leaden paralysis, weight gain, and hypersomnia?

Atypical depression is particularly characterized by specific features such as mood reactivity, where a person's mood can improve in response to positive events. This distinguishes it from other forms of depression where such reactivity is less common. Additionally, individuals with atypical depression often experience leaden paralysis, which refers to a heavy feeling in the limbs that can make movement feel burdensome. Weight gain and hypersomnia—excessive sleeping—are also notable symptoms associated with this subtype.

The presence of these symptoms as a cluster is what makes atypical depression distinct from other types, such as major depressive disorder or persistent depressive disorder, which may not encapsulate the same combination of features, especially the pronounced mood reactivity and specific somatic symptoms. Seasonal affective disorder aligns closely with mood fluctuations related to seasonal changes but does not typically encompass the full range of characteristics associated with atypical depression as highlighted. Thus, atypical depression is the best answer as it succinctly matches this distinctive profile of symptoms.