1. To drain the mental or physical energy from someone. In this usage, a noun or pronoun can be used between "zonk" and "out." Often used in passive constructions. Sitting out in the sun all day really zonked me out! The kids were zonked out after swimming at the beach all day long.

2. To fall asleep or lose consciousness. I can't believe I zonked out on the couch like that! How long was I asleep? Don't zonk out while you're driving—pull over and take a nap if you need to!

3. To intoxicate someone; to alter or inhibit one's senses. Said of drugs, whether prescription or recreational. In this usage, a noun or pronoun is be used between "zonk" and "out." I don't like the way marijuana zonks me out, so I just don't ever smoke it. The pain pills his doctor gave him really zonked Jeff out.