A messed up sleep pattern due to late night studying. Especially among University studentswho study during the night and then get up early for lectures or exams just to fall asleep during the day when they get home. Adjusting after several weeks of late night studying back to a normal sleeping schedule is usually difficult and the student experiences a jet lag even though they haven't been traveling through time zones.
Dude, I can't fall asleep at night, all that exam cramming has given me study jet lag