go to bed
hit the sack
memorize something so well that you can recall it exactly without looking
learn something by heart
very rarely
once in a blue moon
really like sweets and sugary food
have a sweet tooth
feel extremely happy
be on top of the world
begin studying hard
hit the books
be very expensive
cost an arm and a leg
feel ill or not well
feel under the weather
stop yourself from saying something
bite your tongue
