As someone who's experienced recurrent bouts of benign positional vertigo, I can assure you that it's very real, and there's no way anyone with vertigo could possibly play basketball. I could barely walk a straight line, and I had a mild case.
You can dispute whether Gasol really is suffering from vertigo, but not its effects.
As someone who also (very recently) has suffered from that (positional vertigo) I totally agree that there is no way one could play NBA basketball with vertigo.
No way for us to know if Pau's vertigo is positional or something more serious. If it IS positional vertigo, that's usually pretty easily treatable, with simple non-invasive physical therapy. I can't imagine he'd miss more than a few days if it was just that.
There are, of course, far more serious potential causes of vertigo, including heart issues. 'Not something to be taken lightly.