I did the one day Whitney summit thing. Felt great on top. On the descent, both my pardner and I tossed our cookies. Interesting experience.

Later did a trip sleeping successively at Whitney Portal and Iceberg Lake - did not toss cookies - much better

Peter Hackett in Mountain Sickness: Prevention, Recognition and Treatment points out that the altitude at which you sleep is much more significant in achieving acclimatization than the altitude to which you climb.

Just remember that the cure for mountain sickness, especially the potentially fatal acute form, is to descend. Nothin else is as important.