Have you ever had what is called vestibular testing? This usually involves an ENT (Ear, Nose and Throat) specialist and one of the tests is to pour water in your ear and measurement of your eye movements (nystagmus) in response to it. If the testing was abnormal, then it would show the problem to be your vestibular system in your ears. If these tests were normal, then the next step would be to look for neurological causes originating in the brain.
Some of the underlying conditions for a neurological cause are:
Migraine Associated Vertigo
Superior Canal Dehisence
There is much overlap between Meneire's Disease and Migraine Associated Vertigo. Vertigo plays heavily in both of them but Meneire's Disease also has tinnitus and some hearing loss.
The experience that you described as having is similar to what I went through for about three years. Horrible, isn't it? I really empathise with you. In my particular case, I was diagnosed gluten ataxia and migraine associated vertigo. I had extreme problems with vertigo, balance, walking properly and seizures. Migraine associated vertigo does not mean you feel migraine headaches but that it manifests as vertigo. Gtuten Ataxia is where the reaction to gluten proteins takes place in the cerebellum (balance centre of the brain) and your body starts attacking the Pukinje Cells that make up the cerebellum. I've been on a grain free/gluten free/processed food free diet regime for a year and a half and I am now back to normal.
I would strongly urge you to try and get tested for the above conditions if you have not already done so. If there are obstacles in obtaining testing here are some websites that would help in determining the direction you think you should go.
Meneire's Disease Forum
Migraine Associated Forum
Dr. Timothy Haines (North American Renowned Neurologist who works with balance disorders)
The Gluten File (a depository of research articles on gluten ataxia, gluten sensitivity, neurological manifestations of gluten reaction, etcetera)
and of course, here at celiac.com
Hope this helps in some way. Please do remember, that with proper treatment, the vertigo will go away. You won't be stuck like this forever! It might take some diligence on your part at the beginning to start digging and figuring out the causes and what you can do to manage it, but you have already started that process by asking here. Vertigo is not a forever thing and it pays to keep that in mind when you're having a really crappy day and can hardly walk without holding on to walls and you feel your life crashing in on you.
You'll get better. Keep holding onto that.