A deliberate change of sleep pattern with the intention to shift one's peak energy level toward nocturnal activities. Experienced especially after several consecutive nights of drinking and dancing. Etymological origin are the words "jet lag" and to go "clubbing".
Three days after school started I still had difficulties getting up early in the morning because I was still suffering from a severe club lag.
the kind of jetlag you experience not from flying, but from going out clubbing for several days. because you usually stay up until the next morning, and sleep until late afternoon, your biorythm/clock is a bit out of control, just as if you just flew from one timezone to the other. an intensive week-end can already cause you a minor clublag.
"after the week in ibiza, it took us a couple of days to recover from the clublag"