Yes, I have trouble with the dizzy/floating sensations too. It is a pretty awful feeling...so out of control!
I think that it could be caused by a lot of things, or a combination of a couple of them...
Anxiety and improper breathing could be the culprit for sure. When tense, it is easy to hyperventililate which leads to being dizzy. (the chemistry of your blood is actually off, due to a bad balance of oxygen and Co2, causing all kinds of symptoms)
Vertigo can also be a cause of dizzyness. Anxiety does not directly cause vertigo...but if you already have it (common) then stress can make it worse. (positional vertigo happens when you are laying down! So if that is what you mean by certain positions, look up BPPV.)
Sinus, ear, and alignment problems can all be causes, and should be ruled out by the doctor.
There are a lot of causes, almost all of them benign, as you can see. You should make all attempts to find what is causing yours, but if one can't be found, it is probably the anxiety.
Use your breathing techniques twice a day, everyday, and see if that makes a difference:)
Take care, and try not to worry about it (I'll try and do the same!)
"Courage is not the abscence of fear, it is feeling afraid and doing it anyway!"
"It is when we are most lost that we sometimes find our truest friends"
Panic Syndrome recovery due to CBT