Delirium

An illusion is a misperception of a real external stimulus, often in delirium or altered consciousness.

What our notes say

An illusion is a misperception of a real external stimulus, often in delirium or altered consciousness. (Fundamentals of Psychopathology)
Perceptions are intensified in mania, migraine, hallucinogen use and delirium. (Psychiatry Year 6 CAT: June 2023, psychopathology, psychosis, mood and child psy)
Delirium comes on over hours to days, fluctuates, and is usually reversible. (Psychiatry Year 4 CAT: June 2023, schizophrenia, dementia, eating disorders and )
This is a life-threatening exacerbation of hyperthyroidism, presenting with high fever, extreme tachycardia, hypertension, agitation, delirium, and coma. (ENDOCRINE PATHOLOGY)
Neurocognitive: delirium, major neurocognitive disorder (dementia). (Classification of Mental Disorders)
Keep the alternatives open: a mood disorder with psychotic features (mania or depression), substance-induced psychosis (cannabis, khat, alcohol), and a medical or neurological cause (HIV, epilepsy, head injury, thyroid, delirium). (Classification of Mental Disorders)