Is this punishment crazy for a fibbing 5 year old?

My 5 1/2 year old continually fibs in order to get his way........He' ll fake a stomach ache to get out of school, eating, etc. if he thinks he' ll get something better at home, later, etc. Today he faked sick, so now i have told him that he has to stay in bed for the rest of the day, as if he were really sick..............He keeps telling me he won' t fib anymore...I'm sure he understands what the truth is.......Is this way too severe....I' m at my witt's end and this is all i can think of to get him to stop such manipulations........HELP!!!!!