G'day to you too mummymunt.

Is the hyperacusis new, and do you have any known medical condition that has caused this do you think?

Vestibular Hyperacusis can be associated with quite a number of different conditions.
(I know for sure there are many on the Traumatic Brain Injury & Post Concussion Syndrome Forum ).

You could try a forum-wide search for vestibular hyperacusis using the

Forum Search Feature

This is an excellent website discussing many different types of vestibular disorders. It may be helpful for you if you've not found it before.

http://vestibular.org/vestibular-hyperacusis