Depression is a mood disorder that causes a persistent feeling of sadness and loss of interest. Also called major depressive disorder or clinical depression, it affects how you feel, think and behave and can lead to a variety of emotional and physical problems. You may have trouble doing normal day-to-day activities, and sometimes you may feel as if life isn’t worth living.

Symptoms

Although depression may occur only once during your life, people typically have multiple episodes. During these episodes, symptoms occur most of the day, nearly every day and may include:

• Feelings of sadness, tearfulness, emptiness or hopelessness
• Angry outbursts, irritability or frustration, even over small matters
• Loss of interest or pleasure in most or all normal activities, such as sex, hobbies or sports
• Sleep disturbances, including insomnia or sleeping too much
• Tiredness and lack of energy, so even small tasks take extra effort
• Reduced appetite and weight loss or increased cravings for food and weight gain
• Anxiety, agitation or restlessness
• Slowed thinking, speaking or body movements
• Feelings of worthlessness or guilt, fixating on past failures or self-blame
• Trouble thinking, concentrating, making decisions and remembering things
• Frequent or recurrent thoughts of death, suicidal thoughts, suicide attempts or suicide
• Unexplained physical problems, such as back pain or headaches

It’s normal to feel anxious from time to time, especially if your life is stressful. However, excessive, ongoing anxiety and worry that are difficult to control and interfere with day-to-day activities may be a sign of generalized anxiety disorder.

It’s possible to develop generalized anxiety disorder as a child or an adult. Generalized anxiety disorder has symptoms that are similar to panic disorder, obsessive-compulsive disorder and other types of anxiety, but they’re all different conditions.

Symptoms

Generalized anxiety disorder symptoms can vary. They may include:

• Persistent worrying or anxiety about a number of areas that are out of proportion to the impact of the events
• Overthinking plans and solutions to all possible worst-case outcomes
• Perceiving situations and events as threatening, even when they aren’t
• Difficulty handling uncertainty
• Indecisiveness and fear of making the wrong decision
• Inability to set aside or let go of a worry
• Inability to relax, feeling restless, and feeling keyed up or on edge
• Difficulty concentrating, or the feeling that your mind “goes blank”

Schizophrenia is a mental disorder in which people interpret reality abnormally. Schizophrenia may result in some combination of hallucinations, delusions, and extremely disordered thinking and behavior that impairs daily functioning, and can be disabling.

Schizophrenia involves a range of problems with thinking (cognition), behavior and emotions. Signs and symptoms may vary, but usually involve delusions, hallucinations or disorganized speech, and reflect an impaired ability to function. Symptoms may include:

• Delusions. These are false beliefs that are not based in reality.
• Hallucinations. These usually involve seeing or hearing things that don’t exist.
• Disorganized thinking (speech). Disorganized thinking is inferred from disorganized speech.
• Extremely disorganized or abnormal motor behavior. This may show in a number of ways, from childlike silliness to unpredictable agitation. Behavior isn’t focused on a goal, so it’s hard to do tasks. Behavior can include resistance to instructions, inappropriate or bizarre posture, a complete lack of response, or useless and excessive movement.
• Negative symptoms. This refers to reduced or lack of ability to function normally.

Obsessive-compulsive disorder (OCD) features a pattern of unwanted thoughts and fears (obsessions) that lead you to do repetitive behaviors (compulsions). These obsessions and compulsions interfere with daily activities and cause significant distress.

Obsessions often have themes to them, such as:

• Fear of contamination or dirt
• Doubting and having difficulty tolerating uncertainty
• Needing things orderly and symmetrical
• Aggressive or horrific thoughts about losing control and harming yourself or others
• Unwanted thoughts, including aggression, or sexual or religious subjects

A migraine is a type of headache that recurs (keeps coming back), and also causes other symptoms. The pain is often throbbing and can happen on one or both sides of the head. People with migraines can feel dizzy or sick to their stomachs. They may be sensitive to light, noise, or smells.

Migraines can be disabling, and teens with migraines often need to skip school, sports, work, or other activities until they feel better.

Symptoms include:

• have blurred vision
• see spots, colored balls, jagged lines, or bright flashing lights
• smell a certain odor
• feel tingling in a part of their face
• unbearable headaches

Alzheimer’s disease is a brain disorder that gets worse over time. It’s characterized by changes in the brain that lead to deposits of certain proteins. Alzheimer’s disease causes the brain to shrink and brain cells to eventually die. Alzheimer’s disease is the most common cause of dementia — a gradual decline in memory, thinking, behavior and social skills. These changes affect a person’s ability to function.

People with Alzheimer’s disease may:

• Repeat statements and questions over and over.
• Forget conversations, appointments or events.
• Misplace items, often putting them in places that don’t make sense.
• Get lost in places they used to know well.
• Eventually forget the names of family members and everyday objects.
• Have trouble finding the right words for objects, expressing thoughts or taking part in conversations.