Major depressive disorder is characterized by a combination of symptoms that interfere with a person’s ability to work, sleep, study, eat, and enjoy once-pleasurable activities. Major depression is disabling and prevents a person from functioning normally. Some people may experience only a single episode within their lifetime, but more often a person may have multiple episodes. Depressive illnesses are disorders of the brain. The parts of the brain involved in mood, thinking, sleep, appetite, and behavior appear different. Some types of depression tend to run in families. However, depression can occur in people without family histories of depression too.
Signs and symptoms include: persistent sad, anxious, or empty feelings; feelings of guilt, worthlessness, or helplessness; irritability, restlessness; loss of interest in activities or hobbies once pleasurable; fatigue and decreased energy; difficulty concentrating, remembering details, and making decisions; insomnia, early-morning wakefulness, or excessive sleeping; overeating, or appetite loss; thoughts of suicide, suicide attempts; aches or pains, headaches, cramps, or digestive problems that do not ease even with treatment.
Depression (Major Depressive Disorder), Mayo Clinic (Feb. 3, 2018), https://www.mayoclinic.org/diseases-conditions/depression/symptoms-causes/syc-20356007