Sudden diziness, vomiting, loss of

Hello doc My dad is suffering from DM ,HTN,and CAD Recent 2 days back he was alright. Out of no where he started feeling dizzy and was unable to walk properly due to imbalance and he had 2 episodes of vomiting, and he was seeing things upside down at that moment. Later ecg and echo reports are normal. But there was mild lowering of electrolytes.(Na,K,Ca)and was given ig fluids for the same. Then the emergency doc asked us to take ct brain plain and CT pns plain and contrast. CT pns showed mild dns and doctors here diagnosed it was positional vertigo and prescribed tablets betavert ,gemavert,and stemtil. But still there is very little improvement. What next investigation can be done?? And what might be the DD of this case. I am attaching ct  pns film here .