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When you are so tired that you unexpectedly fall asleep causing your head to whips downward then you often whip your head back up again. This usually happens in a seated or upright position.
Wow! Did you just see Seth sleepbang and then smoothly pass it off as listening to punk rock?!
by EssEeeTee April 16, 2018
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When you wake up and bang (coitus) and then go back to sleep.
"I was involved in the sleep bang last night! That is why I can't stay awake at work, boss!"
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by MCLovin2011 January 28, 2017
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