It's an interesting condition, isn't it? And Arapahoe Basin, way above the treeline, is notorious for it when it's overcast and snowing. You can't tell uphill from downhill, can't tell how fast you're going, and without a horizon or any reference to vertical or horizontal, you have to rely on your inner ear and other kinesthetic senses for balance.
But you said you didn't experience any real difficulty skiing it, or keeping your balance, so you did well! I think the vertigo and motion sickness occur because your body doesn't experience the sensations you expect to feel. You think you're going one speed, and you're going faster or slower. You expect to be going downhill, speeding up, but in fact you're going uphill, slowing down. It's weird!
I don't know how to cure the motion sickness and vertigo, other than to get out of the condition and find something to give you some reference points, as others have said. At Arapahoe, stay on the lower mountain, in the trees. Skiing with a group of people can help--ANYTHING that provides an actual reference point can bring your perception back to normal. Kneale's advice to slow down--way down--is good. Make smooth, round turns and keep on turning until you almost stop. Even if you can't tell how fast you're going, and can't tell up from down, it's a sure bet that if you turn far enough around an arc, you'll end up going uphill and slowing down.
As always in less than optimal conditions, good, offensive ski technique is a must. This doesn't mean you need a high level of skill, necessarily. It means you let your skis glide forward, controlling your speed by gliding uphill, rather than with intentional skidding. When you don't know what the snow is going to do--could be smooth, or bumpy, or a big heavy chunk of ice could be lying in wait--you don't want your skis going sideways!
Don't be afraid to open your skis into a small wedge, though. The slight resistance, and the sound, can give you a much better feel for your speed, and if you open your stance a little, it can provide better lateral stability. (It's common to fall to the inside in these conditions, when you tip into what you think is a turn, only to discover that you've actually come to a stop!)
In many ways, skiing these conditions can be good for you--it forces you to tune into important senses that might be dormant when visibility is better. It reminds me all too much that I can be overly reliant on my vision. I was at Arapahoe yesterday with a group of strong intermediate skiers, and we encountered the exact same conditions on top, off the Lenawee lift. At first most people found it disorienting and frightening. But I told them to stay close together and follow me, as we skied slow, smooth, round, very complete turns all the way to the tree line. When we stopped, everyone agreed that it had actually been kind of fun!
As I often say, there are only two kinds of conditions: conditions that are good, and conditions that are good for you! Whiteouts and zero-contrast visibility can be very good for you. But of course, you don't want too much of a good thing. So we stayed on the lower mountain for the rest of the day!
Pretend that it's fun!
[ May 02, 2003, 08:51 PM: Message edited by: Bob Barnes/Colorado ]