Apparently people being examined for insomnia sometimes claim they haven't slept when they are on film with eyes shut, snoring peacefully[citation needed]. I know someone who once thought he had been awake all night, and he had most definitely snored.

I'd not heard of dreaming that one is awake as an explanation, but it sounds reasonable. One can dream that one has got up, dressed, and gone out; and then found it's all to do again when the alarm goes off...

"Schrödinger's Snooze". Love it.