Clue: Before you go to bed, complain to your parents either: you have a headache, you have a temperature, you feel like you're going to vomit or you're aching in numerous places. Take a bowl with you to bed, so "just in case, you'll vomit" and go to sleep. Wake at 20 to 6/7 and complain that you feel worse than before, and it usually works.
Clue 2: Stick a toothbrush in your mouth and make yourself vomit.