The way I described the floaty feeling to someone who's a non-MSer is to ask them if they've ever taken Sudafed or Actifed (before the government took the good stuff out of those cold/allergy medications because of meth-heads) If you've ever taken Sudafed and after that stuff kicks in, it makes your head feel...floaty. Like you just disconnected your head from your neck and it's floating above your shoulders.

That's exactly what that floaty "vertigo" feels like to me, altho it's a lot more disturbing than the feeling Sudafed gives me. But, it was the only way I could really describe it to a non-MSer and have them get some idea of what it felt like.