Charmed,
From what they told me about my mom, it's sort of a deterioration of the inner ear. The doctor said it couldn't be "cured," but it's just a matter of controlling the affects. Mom is 82, totally deaf in one ear and a hearing aid in the other. Yet, she still doesn't hear well.
The actual vertigo comes and goes, so now they just give her a small dose of the meclizine every day and she hasn't had a spell in many months.
I know it has to be awful for your mom. My mom had a spell while sitting in my living room and I was shocked. It literally looked like someone had grabbed her arm and thrown her down as she was getting up from the chair. They don't even have time to brace themselves. Then, with mom, she doesn't remember it happened so doesn't take caution when getting up too quickly. It was really a difficult time.