Oh pinklace, I feel your pain. This used to happen to me ALL THE TIME. I was constantly dizzy and it scared the crap out of me, which of course made me more dizzy, which made me more scared and then more dizzy.
You see? It's a vicious cycle. The fact that you've had a battery of tests performed and nothing has been found points very much to anxiety. That's kind of an unfortunate answer, huh? If it were "something" you could be given a drug or an operation and then you'd be better, but getting over anxiety is a long and arduous process that can involved counseling, medication, meditation, working through your issues, eating better, sleeping better, exercising, an uptick of self care in general; and it will also take TIME. A lot of time, more than you would imagine. Once your stress hormones are pumping and you experience the physical effects of anxiety (in your case dizziness), it takes a long time to get them to pre-anxiety levels. Which means accepting your diagnosis of anxiety and continuing to practice your recovery techniques DESPITE it feeling like you're not making any progress. Yes it sucks and yes we all wish it could be easier, but it's not.
Are you doing anything to address your anxiety already? Talk to your doctor about that and see we what they say.