I would phone your physiotherapist who you saw to do this valsalva manoeuver.

I would suggest it is ear pressure sensitivity. We all do it to some extent when our ears get blocked in airplanes. Yours just sounds as if they've not unblocked and thus the dizziness. It'll probably settle but phone your physio..

I doubt that you have done any harm. There are some other posts across all forums here for valsalva. Not very many though.