When I got up to start work this morning at 6 AM, I found that there was someone covering our East Coast desk this morning, and I could go back to sleep for two more hours. However, it was already daylight of course, so for the first time I tried what some have suggested to me. A relatively light sleep mask (this one was from an airline business-class amenity pack from a long-ago trip) doesn't interfere with my CPAP mask, and I got two more hours of much-needed sleep (inasmuch as I'd had only about four last night due to getting home late and having to be up early.
Thank you to those of you who suggested this. I'll put one of these sleep masks into the Rolling Stone for future use during these long summer days and short summer nights.
Still tired, though. Six hours sleep isn't enough to sleep off a road trip.