Not sure whether it's from the flying or the running, but, my left hip is acting up a little bit. I've chased this problem around in the past - including over a year with doctors - and nothing was ever really diagnosed.
Best guess was a sciatica kind of problem, usually caused by too much sitting.
So, just to be sure I'll take today off and try to get in a gentle run tomorrow. This is the "taper" anyway. A little LESS is better than a little MORE!