I have frequent dizziness, lightheaded ness, and off balance feelings. I had many tests ran, and the conclusion was that I have vestibular migraines (essentially a migraine where the primary ailment isn't pain, but dizziness). The dr said the MRI scans indicated I've had them my whole life, and why they chose to flare up now is anyone's guess. Just for FYI... Vestibular migraines are so common in us that many doctors don't consider them a medical condition, rather a deviation of the human form. Kinda like how some people have better eye sight than others.
With that, the dr put me on topomax at first, which didn't help and made me very irritable. He then switched me to pamelor, which has seemed to help a good bit. I've started having headaches with the anxiety, so he later added depakote to the mix.
Talk to a neurologist and be sure to mention you take the St. John's wort, as studies have shown that it does mess with the serotonin levels in your blood.