I am certainly not a doctor, but I think this may be the condition that Ayu is talking about.
http://vestibular.org/superior-canal-dehiscence-scd#
But I could most certainly be wrong so don't take it as fact. It is only my guess.
I wish Ayu would stop hiding these things!

It's painful to hear her struggling in this way and also bottle it up inside.

I really hope Ayu will buckle down and take things seriously and do as the doctors advise her.
If continuing on the path she is going will cause more damage to her health, I would prefer her to stop doing music. Your health is very important. I don't want her to keep going for the fans if it hurts her well being. Such a tough situation.
Ayu's 20th anniversary is proving to be quite the crossroad for her.