the.com/psychosis

A severe mental state where a person loses touch with reality through delusions or hallucinations.

means A severe mental state in which a person loses touch with reality—through delusions, hallucinations, or disordered thinking.

from Built in the 19th century from Greek 'psyche' (mind, soul, originally 'breath' or 'life') plus '-osis,' a suffix marking an abnormal state or condition — the same ending you see in 'neurosis.' So, quite literally, 'a condition of the mind,' coined by medical writers who needed a clinical word for when the mind's grip on reality slips.

not split personality
that is a different disorder entirely, commonly confused
key features
hallucinations, delusions, disorganized thinking, often temporary
common causes
sleep deprivation, extreme stress, drugs, or underlying illness
treatable
antipsychotics and therapy restore reality testing for most people
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