Thanks Nancy for the concern. Yes, I have had several event monitor and Holter monitor studies.
At first, the Holter monitors seemed to tie the dizzy spells to PACs and PVCs which I apparently still have quite often.
However, after switching cardiologists (due to a change in my insurance network), another month-long event monitor study showed absolutely NO correlations to the PVCs or PACs or any other irregularity of my heart. So, that's when I was referred to the neurologist.
The neurologist didn't feel that the episodes were indicative of TIA activity and thus never ordered an MRI. Instead he focused on wanting to do a lot of tests that my insurance mostly wouldn't go along with and would have cost me a fortune. He was rather strange and esoteric. Therefore, it remains a mystery and I just pray it's not TIA.
One of these days when I get the energy to do it, I'll go see my general practitioner and see if he thinks I should have an MRI.
Sometimes I just have to have a vacation from doctors (although I'm seeing an awful lot of my chiropractor for continuing problems with my back which never fully abated after the heart surgery).
I find J.B.'s comment above interesting, as my left eye also often "goes dark" or fails to focus during these episodes.
The migraine associated vertigo may also be a clue. By the way, that link is
http://www.emedicine.com/ent/topic727.htm