1. Fall asleep fast, as when one is extremely tired
   "after the long drive, we zonked out and slept for 10 hours";
   - zonk [informal]
    
2. Lose consciousness due to a sudden trauma, for example
   "He zonked out from exhaustion after the long hike";
   - pass out, black out, zonk [informal]

Derived forms: zonks out, zonking out, zonked out

Type of: change state, dope off [informal], doze off, drift off, drop off, drowse off, fall asleep, flake out [informal], nod off [informal], turn