I did some research to address your situation. As you well know, but other readers may not, subjective vertigo is the sensation that you are moving.
Vertigo has a few causes:
inflammation of the inner ear
decreased blood flow to the base of the brain
symptom of associated with migraine headaches and multiple sclerosis
complications of diabetes can lead to artherosclerosis, (hardening of the arteries) which decreased blood flow to the brain
You said that you have been tested but no cause has been identified. Has your doctor prescribed any treatment. There are medications used to treat vertigo. These include Antivert, Benedryl. Transderm Scop, Phenergan and Valium. These medications should only be taken as directed and under the supervision of a physician.