September jet lag
The tiredness you get for about a week after starting school again because your body clock is still running in the 'summer holiday' time zone. Typically caused by sleeping at 3am everyday for two months and waking up the next afternoon.
Awake Student: Could you lift your snoring head off my shoulder? You're drooling on me here.
Sleepy Student: *yaaaawwwwnnn* Sorry, I've got September jet lag real bad, I practically sleep-walked here in the first place.