Several patients even experienced hallucinations, including transient “Capgras delusion,” a psychiatric disorder in which a patient starts believing that a close friend or family member was replaced by an impostor.

“He had delusions, hallucinations, weight loss, aggression, repetitive speech,” Ellis’ son Steve told the BBC.

At first, Ellis’ doctors suspected it was a case of Creutzfeldt-Jakob disease (CJD), a fatal and rare degenerative brain disorder.