What Is Mental Illness?

What Is Mental Illness?

Mental health includes our emotional, psychological, and social well-being. It affects how we think, feel, and act, and helps determine how we handle stress, relate to others, and make choices.

Mental illnesses involve changes in thinking, mood, and/or behavior. These changes can affect how a person relates to others and makes choices, and can impact day-to-day living and a person’s ability to function.

Mental illnesses are treatable medical conditions. These conditions can range from mild to severe, and are common, recurrent, and often serious, but they are treatable.

What Causes Mental Illness?

Mental illness is no one’s fault.

Having a mental illness is not a choice, a weakness, or a character flaw. It is not something that just “passes” or can be “snapped out of” with will power. It does not mean that a person is broken or that they, or their family, did something “wrong.”

Mental illness isn’t the result of one event. Research suggests that multiple, linking factors can play a role in whether a person develops a mental health condition. These factors include:

  • Genetics and family history
  • Traumatic life events
  • A stressful job or home life
  • Environment and lifestyle
  • Biochemical processes and circuits,
    and basic brain structure
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Who Develops Mental Illness?

Mental health conditions affect people from all walks of life and all age groups. They're far more common than you might think.

In the United States, in a given year:

  • 1 in 5 adults – 57.8 million people – experience some form of mental illness.
  • 1 in 20 adults –14.1 million people – experience serious mental illness.
  • 1 in 6 youth (ages 6-17) experience a mental health disorder.
  • 50% of all lifetime mental illness begins by age 14, and 75% by age 24.

Despite how common it is, stigma and judgement prevent many people from seeking needed treatment. Estimates suggest that only half of people with mental illnesses receive treatment, and the average delay between onset of symptoms and treatment is 11 years.

Left untreated, mental health conditions are among the most disabling and destructive illnesses. It’s important to normalize talking about mental health so people can feel empowered to seek the help they need.

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Warning Signs and Symptoms

What kinds of feelings, thoughts or behaviors are a signal to get help? Though each condition has its own symptoms, common signs of a mental condition can include:

  • Excessive worrying or fear
  • Feeling excessively sad or low
  • Confused thinking or problems concentrating and learning
  • Extreme mood changes, including uncontrollable “highs” or feelings of euphoria
  • Prolonged or strong feelings of irritability or anger
  • Avoiding friends and social activities
  • Difficulties understanding or relating to other people
  • Inability to carry out daily activities or handle daily problems and stress
  • Inability to perceive changes in one’s own feelings, behavior or personality
  • Multiple physical ailments without obvious causes (such as headaches, stomach aches, vague, ongoing aches and pains)
White man sitting on couch in black sweater with hand on head stressed out
  • Changes in eating habits such as increased hunger or lack of appetite
  • Changes in sleeping habits or feeling tired and low energy
  • Thinking about suicide
  • Difficulty perceiving reality (delusions or hallucinations, in which a person experiences and senses things that don’t exist in objective reality)
  • Overuse of substances like alcohol or drugs
  • An intense fear of weight gain or concern with appearance

(Young children may experience different kinds of symptoms. Learn more at NAMI.org)


If you’re experiencing changes to your thoughts, moods, or body that make it hard to manage work, school, home, or relationships, and those changes have lasted for more than 2 weeks, it may be time to ask for help.

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How Do You Know When To Be Concerned?

It can be hard to tell if what you're experiencing goes beyond typical stress or worry. It might be helpful to think about your mental health in the same way you think about your physical health.

Think about having a stomach ache because you ate too much or too fast. It causes discomfort, but you manage it by taking an over-the-counter medication or changing how you eat. It doesn’t last too long, and you probably wouldn't be concerned that something was seriously wrong.

But what if you wake up with a stomach ache every single day? You might try to manage it by taking over-the-counter medications or changing your diet. But when the pain doesn't go away, and it starts getting in the way of work, school, or sleep, this persisting pain would alert you that something is wrong.


Now, imagine that instead of a stomach ache, you’re feeling anxious. An anxious feeling can be temporary – maybe there’s an upcoming meeting or exam that you need to prepare for. But if the anxious feeling doesn't go away, and it starts to significantly interfere with your daily life, this can indicate an underlying health condition.

You don’t need to know exactly what's wrong to decide that it’s concerning enough to seek help.

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Getting A Diagnosis

Unlike diabetes or cancer, there is no medical test that can accurately diagnose mental illness.

To receive an accurate diagnosis, a doctor should evaluate you to rule out possible underlying physical conditions that could be causing symptoms.

Once physical ailments are ruled out, you may be referred to a mental health professional who will interview you about your history of symptoms, and use The Diagnostic and Statistical Manual of Mental Disorders, to make a diagnosis. Published by the American Psychiatric Association, the manual lists criteria, including feelings, symptoms and behaviors over a period of time, that a person must meet in order to be officially diagnosed with a mental illness.


A diagnosis is an important tool. Doctors and therapists use a diagnosis to advise you on treatment options and future health risks. It tells health insurance companies that you have a condition requiring medical care. It’s also necessary to qualify for Social Security disability support or for job protection under the Americans with Disabilities Act.

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Mental Health Conditions and Related Components

Learning about a mental health condition can be a good step toward finding effective treatment that can reduce or eliminate symptoms, and improve quality of life.

Find information about these mental health conditions -- symptoms, causes, diagnosis and treatment -- at NAMI.org.

Related Components of Mental Illness

Certain conditions are often related to mental illnesses. These conditions may be a cause or symptom of a mental illness, or be a condition that can increase the likelihood of a mental illness developing.

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Mental Illness Myths vs. Facts

Trusted Sources for More Information

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In crisis? Call or text 988.   For non-emergency guidance, contact the NAMI Jacksonville Helpline: 904-323-4723 or email Helpline@namijax.org

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