Urgent help: Diziness & headache | 50y.

Hi, my mother is 50yrs and had diabetes, hypothyroidism and hypertension. Recently since February, she has been facing serious dizziness and headache (left side). The dizziness is all of a sudden and she describes it as everything going round in speed. She happened thrice in the gap of few weeks and now is regular. It happens when she is sleeping or gets up or looks around. Past one month, we showed one GP, who gave vertigo medicine for 3-4 weeks but it wasn't better (she used to feel okay for the time being). Then we showed a specialist GP who gave another set of medicines and changed the BP medicine (we are on the 14th day now). But there is very less improvement. Please help me I understanding what should I do next? What is this called? Do we need a brain scan? What is the best medical help here?