To be unconscious or in a deep sleep. Likened to a boxer who has been knocked out. I didn't even hear you come in last night—I was so tired that I was out for the count as soon as my head hit the pillow.On his 21st birthday, Mike's friends gave him so much to drink that he was out for the count by 10 PM.The rowdy customer was out for the count when the bouncer punched him in the head.
Usage notes: When boxers (= men who fight as a sport) are still not conscious after ten seconds have been counted they are described as 'out for the count'.
I was out for the count so I didn't hear any of it going on.