Thanks for your query.
Noted the history and understood your concerns.
With the history of motor vehicle accident, thyroid
problem the history of dizziness
can be due to multiple problems as follows:
If the accident involved head or mastoid area, there can be disruption of the semicircular canals and thus causing dizziness and the nausea is usually secondary to it.
Other reasons can be: Electrolyte imbalance
Cervical spondilitis primary or enhanced by accident.
I would advise you the following in such a situation:
Yes, this needs urgent emergency care for clinical evaluation, examination and relevant investigations like MRI
of the brain, mastoid, cervical and as needed.
This will give the most probable diagnosis and thus the symptomatic as well as well as definitive treatment.
Specialist's opinion like Neurophysician and an ENT Surgeon may help further to identify the proper cause and get the correct accordingly.