Hello dear, Considering the fact that your dad had undergone a brain surgery and he is also taking medication for BP and diabetes, the symptoms can be attributed to either a residual effect of the surgery or any sudden fluctuation in BP/ blood sugar levels. In addition, vertigo is also seen due to pathology in the Vestibular Apparatus in inner ear (it is associated with maintenance of body posture & balance) most probably Labyrinthitis or Benign Paroxysmal Positional Vertigo. Symptomatic relief can be obtained with intake of Vestibular sedatives like Betahistine or Cinnarizine preparations (to be taken only under the guidance of a Physician). If it still persists, then you need to consult his treating doctor Physician/ ENT Specialist & get a complete clinical examination done. Investigations like estimation of blood pressure, blood sugar levels, serum electrolytes & vestibular function tests will be required to rule out any pathological cause for the symptoms. There is no need to worry, he will be fine. Till then, he should maintain adequate hydration & proper nutrition status and avoid stress. And also take precautions of getting up from bed slowly & avoid sudden head movements. Wishing him a Good Health. Take care.