Thanks very much, Bob, for this thorough advice. I have a prescription for Diamox coming, and will begin taking it a day before my next trip.
In my case, symptoms are almost always the same: seemingly sudden onset of a rapid and thready pulse, quick fatigue, and the desire to take a nap, as though someone had just pulled the plug on me-- not the kind of ordinary, slowly developing fatigue one might experience just from effort. If I stay at altitude, the pulse stays elevated, easily over 120, then overnight diminishes, leaving me somewhat spent.
This last weekend, starting at Road's End and heading toward Avalanche Pass, with 29 pounds, (19 of it food),I was doing great through the switchbacks to Sphinx Creek Junction, and well on the switchbacks and stairs just past the junction, but a mile or so into the forest, just as I reached the small creek which crosses the trail, (at about the same altitude as where Sphinx Creek crosses the trail, probably about ~8400'), I was suddenly wiped out, pulse thready and over 120, though breathing normal, and had to flog myself to get to a campsite near Sphinx Creek.
Had I done day hikes to altitude beforehand, like Alta Peak or Jenny Lake out of Stony Creek, I'm sure I would have been fine, as, just three weeks earlier, having done Alta, two days before, (with similar symptoms at 11,000' --not carrying weight) I comfortably got to Sphinx Lake at 10,500', in a day, with only mild distress at 8400', which I dealt with by taking a nap.
Will also order a pulse-oximeter. Notice that Amazon carries them.
Sorry if this is too much detail for the general reader here, but Bob doesn't have a PM set up yet, and perhaps this is useful to others.