When you smoke so much weed or some amazing weed and you wake up the next morning your still high.
Yah man, after that fat sack last night I woke up this mornin with a stone over.
Excuse invented by stoners to avoid doing any work. Similar to a hangover but induced by cannabis. Such excuses avoid questions from friends about long term job options or possibly, when the next illegal rave is.
I havn't been into school this week because i've woken up at 3pm with a massive stone over.