Severe sadness that comes on suddenly, and is either (a) too severe for the circumstances or (b) exists without any external cause, is called

_____ is a mood disorder that is caused by the body's reaction to low levels of light present in the winter months.

Theorists who adopt the behavioral perspective link depression to

Severe sadness that comes on suddenly, and is either (a) too severe for the circumstances or (b) exists without any external cause, is called