Mine comes on really suddenly, and very strong. One time, I was just laying on the couch and fell off!
It feels like being on a boat on serious waves. Only once (maybe twice) did I feel nauseous - but then, I don't get that even with really bad migraines, I'm lucky.
I was checked by ENT, too, also okay.
Neuro does not know what's up with me, no meds, I did not want any.
Oddly, it seems okay when I drive. If it's bad sitting still, it's bad walking, but better - like gone - if driving? I heard about something called Disembarkment syndrome, where that happens. Would ask my doc, but right now I'm in that *hate all drs* mode. Rather drop dead than talk to one, lol.
How to cope? Careful on the stairs, don't carry anything fragile, and look across the room at something when walking - focus. Never look down, to look down is to throw the balance off more. And sippy cups.