Depression:

A low, sad state in which life seems bleak and its challenges are overwhelming. Symptoms to look for include, a persistent sad, anxious, or empty mood. Feelings of hopelessness, pessimism, feelings of guilt, worthlessness, helplessness, restlessness, irritability. Loss of interest or pleasure in hobbies or activities that were once enjoyable. Decreased energy, fatigue, being slowed down, difficulty concentrating, remembering or making decisions. Insomnia, early morning awakening, or oversleeping. Changes in eating patterns, either overeating or loss of appetite.