Hallucination. His hallucinations.

My father age 78yrs had an issue of unsteadiness and then he fell in washroom leading to an injury on head and had stiches. His ct and mri taken after the injury are normal. Later he took only one tab vertin 8mg tab given for unsteadiness . 24hr after taking the tab he had delirium and confusion which subsided automatically the next day. He stopped vertin thereafter. His serum electrolytes are normal. Then he was normal for 2 days and again he was prescribed with vertin 16mg tid. Now he is having visual hallucinations.His memory is normal. And the doctor asked to stop all the medications but his symptoms did not subsided. He is knowm hypertensive and is on medication but his bp slightly rised to 150/90. Known hypothyroidism taking 100 microgram thyronorm but his TSH is slightly elevated to 7.1. Not a known pt of diabetes. No history of fever headache vomitings. CBP CUE are normal. Can you please tell us the reason behind his hallucinations.