"I seem to recall the increased permeability of lung tissue (something helps deliver oxygen to the tissues but that can go awry in HAPE) was in the 1-2 week range."
You have to get a certain air pressure in your lungs for the alveolar membrane to pass oxygen across into the capillaries where the red blood cells are being pumped along, and the blood pH has to be sort of correct for the oxygen to want to latch onto the hemoglobin. Then it gets pumped out to your muscle tissues for use. There, carbon dioxide latches onto the "empty" hemoglobin where it is returned to the lungs. That is where odd things can happen. If the blood pressure and pH _are_ right, the carbon dioxide will unlatch, transfer across the membrane into the lungs, and then get exhaled. If the blood pressure and pH are _not_ right, the carbon dioxide can fail to unlatch or transfer, and it "takes another ride" around the loop. That dramatically decreases the overall efficiency of respiration. So, once that happens, it is a vicious cycle, so the victim feels bad and then gets progressively worse. You will see a drop in oxygen saturation in the blood if you have an oximeter handy.
If you are a big believer in luck, then you just wait for it to get better. In some cases, the victim will recover automatically, even at some moderate elevation. In other cases, the victim will not recover on his own, and intervention is necessary. The old axiom applies: Go down, go down, go down. There is a lot of evidence that taking the victim down 3000 feet will save his life, and it is best to make that happen while the victim can still move under his own power and before he becomes a statistic.
Incidentally, if you drive too far from sea level up into the mountains for your first night, you might trigger this whole problem right there before you ever get onto the trail. That's why sleeping in your car at some 11,500 foot trailhead might not be smart.