Herpes simplex encephalitis has a mortality of 70% untreated and 20% even with treatment — IV aciclovir must be started empirically before LP results in any patient with fever + confusion + hallucinations. Delirium tremens carries 5% mortality — alcohol withdrawal hallucinations require same-day admission for chlordiazepoxide regime. Antipsychotics in Lewy body dementia/Parkinsonism cause severe neuroleptic sensitivity reactions (irreversible Parkinsonism, NMS) in up to 50% of patients — this is a contraindication that must be remembered.

Modality guides the differential powerfully: visual hallucinations in an elderly patient with poor vision and intact insight almost always represent Charles Bonnet syndrome (benign) — no investigation is needed beyond reassurance. Olfactory hallucinations (unusual smells with no external source) are the most strongly associated modality with organic brain pathology — temporal lobe epilepsy (uncinate fits), brain tumour, or psychiatric illness. Third-person auditory hallucinations (voices talking about the patient in third person) are a first-rank symptom of schizophrenia (Schneider, 1959). Hypnagogic/hypnopompic hallucinations at sleep transitions are experienced by 25–37% of normal population and require no investigation.

Lewy body dementia is the second most common dementia (after Alzheimer's) and is characterised by vivid formed visual hallucinations (often small people or animals), cognitive fluctuation, and Parkinsonism. It is critically important to recognise because antipsychotics are severely contraindicated. Grief hallucinations (experiencing the presence, voice, or vision of a deceased loved one) affect 50–80% of bereaved people — this is a normal bereavement phenomenon and should be normalised, not investigated. PTSD hallucinations are re-experiencing phenomena (flashbacks) rather than true hallucinations — they respond to trauma-focused CBT, not antipsychotics.

The 4AT is the most validated delirium screening tool for primary care (sensitivity 76%, specificity 94%) and takes under 2 minutes. Wernicke's encephalopathy triad (confusion + ataxia + ophthalmoplegia) is rarely complete — any two features in an at-risk patient (alcohol dependence, malnutrition) should prompt immediate IV Pabrinex. Untreated Wernicke's progresses to irreversible Korsakoff's syndrome in 80% of cases — early treatment with thiamine is curative. Papilloedema on fundoscopy in a patient with hallucinations and headache mandates same-day CT head (raised ICP).

Anti-NMDA receptor encephalitis is critical to recognise — it presents most commonly in young women (20s–30s) with psychiatric symptoms (paranoia, hallucinations, agitation) before developing seizures and movement abnormalities. It is treatable with immunotherapy (steroids, IVIG, rituximab) and associated with ovarian teratoma (50% of cases) — early recognition prevents permanent neurological damage. Hyponatraemia (<125 mmol/L) causes hallucinations and confusion — U&E are mandatory in all presentations. Hypoglycaemia is instantly reversible — check blood glucose at the bedside immediately.

Treating the underlying cause resolves delirium in the majority — physical restraint and sedation should be minimised. Rivastigmine reduces visual hallucination frequency by 30–40% in Lewy body dementia through acetylcholinesterase inhibition — this is the treatment of choice. Haloperidol in Lewy body patients causes severe extrapyramidal reactions in up to 50% — this represents one of the most important drug contraindications in geriatric medicine. IV Pabrinex contains a higher concentration of B vitamins than oral thiamine and must be given IV/IM (oral absorption is unreliable in alcohol-dependent patients due to gut malabsorption of thiamine).

Charles Bonnet syndrome is frequently misdiagnosed — patients are often too frightened to report hallucinations for fear of being labelled "mad" or admitted. Simple psychoeducation (explaining the benign nature of the visual filling-in process) resolves distress in the majority without any pharmacological treatment. Sleep deprivation is an underrecognised cause of hallucinations — it lowers the threshold for psychotic symptoms and can precipitate episodes in vulnerable individuals. Improving vision in Charles Bonnet often eliminates hallucinations completely — cataract surgery represents one of the most effective "hallucination treatments" available.

The single most important monitoring question after treatment of drug-induced hallucinations is: "Did they resolve when the drug was stopped?" — failure to resolve confirms a primary neurological or psychiatric cause requiring further investigation. Wernicke's encephalopathy can develop acutely in any patient with alcohol dependence — even brief periods of poor nutrition (illness, hospital admission) can precipitate it. Recognition of the nystagmus + ataxia + confusion triad allows immediate IV thiamine treatment before irreversible Korsakoff's syndrome develops. Ongoing safety-netting for the carer of a patient with dementia-related hallucinations is as important as patient safety-netting — carer crisis is a common cause of emergency admissions.