Rod, I'm sure severe, deadly cases of HAPE or HACE don't happen nearly as often in the Sierra as they do in the Himalaya or other higher ranges, but I know from personal experience that it happens. Unfortunately it happened to someone I ran across at Cottonwood Lakes last August.
A teenage boy (16, I believe) hiking with a group. I stopped to chat with them for a while, and the boy was definitely suffering from a bad case of AMS (killer headache, nausea, lethargy, dizziness). His friends didn't seem that concerned about him, but I strongly suggested they get him back down to Horseshoe Meadow and then on to Lone Pine. They said they'd watch him and make a call about what to do a little later in the day. We chatted for a while about taking an easy pace, hydrating, eating, etc. All they had for headache was Tylenol, so I left some Advil with them and went on about my hike.
I was shocked to read in the Inyo Register the next day that the boy had to be medi-evaced out and was DOA at the hospital from "AMS", which I'm sure was probably HACE or HAPE. Hours after I left that group, the boy was dead from the altitude at "only" 11K'.
If I had had dex with me, would I have left some with them? I don't really know, in retrospect. The kid was suffering, but it looked like the same thing my wife expereinced her first trip up to 14K' (Pikes Peak). She was fine after getting back down to 7K' (quickly!), and the one personal experience I've felt with AMS went completely away once I descended about 2500 feet. I certainly didn't think this boy's life was in danger but, now that I have that experience in my rearview mirror, I may act differently in the future (assuming I ever have any dex with me, which is a big if).
That experience has definitely changed my perception about AMS - I always thought of the deadliness of AMS progression as being pretty much in the 20K' and above climbing world, but I see it a little differently now.
