It sounds just like antidepressant withdrawal. That was my worst symptom when I quit taking Cymbalta. I also tried to taper down the dose the but dizziness lasted for months. It did get better with time. Hang in there!
How long did you take to do the step-down? Sometimes it takes longer than a couple of weeks, which is why I'm scared to go off Effexor. But, if you continue to have the dizzy feeling, contact your doctor. Peace of mind makes a big difference. One of the unfortunate things about this disease is you can never again take a "different" feeling for granted. Congratulations on the normal CA 125. Please come back and let us know how you progress.
My condolences to you on the loss of your sister-in-law.
Gail