CincyPaul,

Welcome to NeuroTalk.

Your husband's flare up from turning quickly may indicate he has an upper neck injury that has never been addressed. 80% of concussions include an upper neck injury.

Gentle physical therapy, gentle chiropractic, and discipline with his posture when he sleeps.

He could also have an inner ear issue. The Epley Maneuver may help. Most PTs and vestibular Therapists can help with that. YouTube explains what the Epley Maneuver is. Crystals can become dislodged in the ear and cause sensations that overwhelm the brain and vestibular system.

Other than finding a subtle neck injury or vestibular disorder, treating the symptoms is the standard. There is no standard treatment for brain injury or concussion. You treat the symptoms.

Vision issues can also cause nausea as the eyes are a big part of balance. A behavioral optometrist can often help. There is a clinic in Chicago that is the best in the country.
The Mind-Eye Institute : Neuro-Optometric Rehabilitation

Hope this helps.