A 67-year-old female presented with post-ganglionic Horner's syndrome. In addition to the classical symptoms of Horner's syndrome, the patient reported experiencing frightening complex visual and auditory hallucinations on two different occasions. Magnetic resonance angiography of the cerebrum, neck and upper thorax revealed internal carotid dissection. The symptoms and hallucinatory experiences resolved soon after antiplatelet therapy was commenced. We propose peduncular hallucinosis as the underlying mechanism.