zonk out

verbs

lose consciousness due to a sudden trauma, for example
black out, pass out, zonk out
fall asleep fast, as when one is extremely tired
"after the long drive, we zonked out and slept for 10 hours"
zonk out
is a type of (narrower)
change from a waking to a sleeping state
"he always falls asleep during lectures"
dope off, doze off, drift off, drop off, drowse off, fall asleep, flake out, nod off