I have also been in an accident where my Speedplay X pedals automatically released. Because I hit my head, I don't remember any of the flying upside down part, but the bike and I were a several feet apart when I found myself on the ground with a broken clavicle. I doubt that the pedals release just because you are upside down, since the mechanics are very simple. Maybe they release at a high enough force or impact. Look and SPD pedals have an adjustable tension setting (too light and you might come out while pedaling hard, too tight and you might not get out when you stop).
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72