I had vertigo that would hit me like that back in 2007.

It felt like it came up my left side, would swirl around my head to the right and make me want to fall down. Felt like a wave sweeping over me.

I had oral steroids (yuck! Oral pred tastes nasty!) and that particular type of vertigo has only come back once and that was earlier this summer at the start of my vision problems that I just had IV steroids for.

Does it happen when you look in a certain direction, or when you're reading? maybe it could be visually induced?? (I think mine was caused by some sort of vision problem when looking to the side...but that's just because I was usually reading when it happened)