Anosognosia

When someone rejects a diagnosis of mental illness, it’s tempting to say that he's “in denial.” But someone with acute mental illness may not be thinking clearly enough to consciously choose denial. They may instead be experiencing “lack of insight” or “lack of awareness.” The formal medical term for this medical condition is anosognosia, from the Greek meaning “to not know a disease.”

When we talk about anosognosia in mental illness, we mean that someone is unaware of their own mental health condition or that they can’t perceive their condition accurately.

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What Causes Anosognosia?
... updating process is complicated. It requires the brain’s frontal lobe to organize new information, develop a revised narrative and remember the new self-image.
Brain imaging studies have shown that this crucial area of the brain can be damaged by schizophrenia and bipolar disorder as well as by diseases like dementia. When the frontal lobe isn’t operating at 100%, a person may lose—or partially lose—the ability to update his or her self-image.

Without an update, we’re stuck with our old self-image from before the illness started. Since our perceptions feel accurate, we conclude that our loved ones are lying or making a mistake. If family and friends insist they're right, the person with an illness may get frustrated or angry, or begin to avoid them.

Anosognosia affects 50% of people with schizophrenia, and 40% of people with bipolar disorder. It can also accompany illnesses such as major depression with psychotic features. Treating these mental health conditions is much more complicated if lack of insight is one of the symptoms. People with anosognosia are placed at increased risk of homelessness or arrest. Learning to understand anosognosia and its risks can improve the odds of helping people with this difficult symptom.

Why Is Insight Important?
For a person with anosognosia, this inaccurate insight feels as real and convincing as other people's ability to perceive themselves. But these misperceptions cause conflicts with others and increased anxiety. Lack of insight also typically causes a person to avoid treatment. This makes it the most common reason for people to stop taking their medications. And, as it is often combined with psychosis or mania, lack of insight can cause reckless or undesirable behavior.

Additional information at the link.

https://www.nami.org/Learn-More/Mental-Health-Conditions/Related-Conditions/Anosognosia