One of sleep apnea's unfortunate outfalls is atrial fibrillation. Happened to me. Not a sure thing, not for everyone, but it is common enough that cardiologists will ask their patients to take an at-home test or to go to a sleep lab over night if there are no obvious signs of ischemia.

Your stated pulse rate is quite high for just walking. When I climb all 300+ steps at our local ocean-side bluff known as the Goose Spit Steps, my HR climbs only to about 144 by the time I am 2/3 of the way up. This isn't a quick pace, but a steady and unbroken assault on the bluff until I reach the top. I don't want to stress my already addled heart unduly, and when using the formula for Max HR based on one's age, I'm right at the max of 220 (age plus HR = Max HR). If you are reasonably fit, not above BMI 26, And under 50 or so, a walking pulse of 160 might indicate AF. This is likely because you claim that it is not only rapid, and weak/hard to detect, but it is irregular...the classic sign of AF. This would account for your weakness, and probably some breathlessness as well..?

For your sleep apnea, you should know what your weekly and monthly averages are for your AHI (apnea-hypopnea index(. You need to poll the data on your machine's SD card. If it doesn't have a card, get any standard SD card from your local drug store or digital supply outlet with at least 2 gigabytes of data capacity. Even so, your machine should tell you on its display each morning.