We're glad to hear that you made the right decision and descended.
Diamox might help, but you ought to try at in a less challenging altitude before using it at Whitney...just in case you don't like the side-affects. Perhaps try it on some high-altitude hikes in Alaska; you've got some big mountains up there.
You might consider camping at the Whitney Portal camp ground for several nights (more than two) before starting up the trail.
Also...and this is very important...watch the local weather forecasts very carefully. Major storms can and have occured at the end of September. Storms at Whitney can prove to be deadly. The Sierra Nevada isn't always "gentle" in the Fall and Winter.
