A microsleep is when we fall asleep for the briefest of moments, so brief in fact, that we might not realise it has happened.

Stage 2: After 36 hours of no sleep, your attention span shortens, your reaction time slows, your vision may be blurry, and you may have microsleep ... your desire to fall asleep is intense ...

"Circumstantially the most likely explanation action is that Mr Jackson had fallen asleep," he added. "Mr Jackson drifted across the road into the path of Ms Davies during a moment of microsleep ...