Herceptin - can it cause Vertigo?

I have been on Herceptin since June 30, 2004 - only three infusions to date. After the first treatment I developed vertigo which improved, after the second treatment the vertigo was mild but now after the third treatment it seems to be much worse. It is triggered by movement or walking much like positional vertigo. I am taking no other chemo at this time and am Stage 2b. Have any of you experienced vertigo while only on Herceptin?