I may as well add this to the data base as one more sleep "incident". As a few others have reported, the Vox was just sitting here in sleep mode, when the screen blinked on and off. FWIW, I have the WiFi always off (airplane mode) when I don't need it.
This momentary awakening caused no problem. Who knows, maybe it happens quite often because I usually have the book cover closed, but this time it was open.