zonk out vs drowse off

zonk out and drowse off both are verbs.

Word	Noun	Adjective	Verb	Adverb
zonk out	No	No	Yes	No
drowse off	No	No	Yes	No

As verbs, drowse off is a hypernym of zonk out; that is, drowse off is a word with a broader meaning than zonk out:

Other hypernyms of zonk out include dope off, doze off, drift off, drop off, fall asleep, flake out, nod off.

zonk out (verb)	drowse off (verb)
fall asleep fast, as when one is extremely tired	change from a waking to a sleeping state
lose consciousness due to a sudden trauma, for example