Anxiety disorders encompass excessive anxiety, which is based on the experience of fear, shared with other animals. Fear is the behavior under external, imminent danger: the body experiences a surge of adrenaline in situations requiring escape or defense of oneself, leading to the arousal state of “fight or flight”
Depression is the state of feeling unhappy, “being down in the dumps”, or having “the blues”, with the associated feelings of feeling unmotivated, and not feeling satisfied with things that ordinarily are naturally enjoyable, such as eating, sleeping, concentrating on things, exercising, or positive life events. Other associated feelings are feelings of low self-esteem, excessive guilt, feeling tired moving and thinking, and thinking more about death.
At the center of the illness is at least one manic or hypomanic episode. A manic episode is a distinct period of unusually elevated, expansive, or irritable mood accompanied by increased goal-directed activity or energy, lasting at least 1 week and present most of the time.
Obsessive-compulsive disorder (OCD) is characterized by either obsessions or compulsions. Obsessions are unwanted repetitive thoughts, images, or impulses that the patient has, often themes of threat or danger, and which cause significant distress.