During a car accident nearly four years ago, I suffered two brain bleeds and now have a focus of encephalopothy in my frontal lobe. Since then I have been dizzy some or all of every single day. Message, vestibular exercises, Tai Chi, reading books not newspapers or tablets because with books one's head stays stable, doing music and painting and socializing on a small scale have all helped me.
Your husband having dementia definitely complicates things, but music and slow movement exercise like Tai Chi would help, I believe. Eye movement training from a Physical Therapist may help also. Lorazepam in small doses has helped me maintain, although it is an addictive substance and use of the drug needs to be monitored. My hope for you and your husband is to take small steps each day toward healing. Good luck.