Balance, vestibular, and cognitive issues after getting ill

In sum, I have had 3 concussions in my life, the last in '16. Since then I have had the above issues that are triggered by illnesses that have a fever, being on a boat for an extended period, and in multi sensory environments like a concert. I then need to go through balance and visual therapy which in time helps me get better. But, I relapse easily with these activities. My dx is mild traumatic brain injury, and inner ear issues have been ruled out. Again, I am so confused as to how these differing trigger events can all cause the same symptoms. Obviously I can't avoid all of those activities but the consequences are tough to take at my age 63. If anyone has any insights here I'd certainly appreciate it!