Another possibility is not enough cerebrospinal fluid [CSF] in the brain and/or spinal cord. This may be due to a leakage, trauma [rupture], radiation, chemo therapy [including spinal tap/intrathecal therapy/ lumbar puncture] or because for some reason your body is no longer producing enough CSF.
Some inner ear problems/infections can also produce these symptoms. As can some classes of antibiotics [e.g. erythromycin].
Try to chronicle all of the events [overall health, illnesses/infections, meds/supplements, diet, sleep, exercise, activities, weather, travel, etc.] from about a month before your symptoms first appeared to the present day. Include everything and try not to second-guess yourself while doing this. I have used this method and have found it very useful in helping to narrow the probable causes.