To sleep.
It can also be used as an adjective "schlumphy" to describe the feeling of being extremely tired or sleepy.
Can alternatively be spelled schlümph, using the German umlaut above the <u>.
Origin: A malapropism formed accidentally in a moment of extreme tiredness, by an American, combing the German word for sleep "schlafen" with the German word for a Smurf, "schlumpf".
"I need to schlumph before the party."
"No, I can't go out; I'm way too schlümphy to drive."
"Sorry I missed your call; I was schlümphing."