This petition was rejected

The Government e-Petitions Team gave the following reason:

We can't accept your petition because the naming of health conditions is not the responsibility of the UK Government or Parliament.

We're also not sure what you mean by "classed as a disability". Laws and policies, including the Equality Act and the PIP assessment process, don't list specific conditions and define them as disabilities. In most cases, it’s the impact that a health condition has on the person’s life that qualifies them for support or protection under the law.
 
You can find out more about showing that you're disabled under the Equality Act here:  

www.citizensadvice.org.uk/law-and-courts/discrimination/protected-characteristics/showing-you-re-disabled-under-the-equality-act/

You could start a new petition calling for a Government funded campaign to raise awareness of vestibular disorders if that is something you would like to see happen.