Feel under the weather
Be sick
Pull someone's leg
Joke with someone
On the ball
Do a good job
As busy as a bee
Very busy
Cry over spilt milk
Get upset about something unimportant
Cost an arm and a leg
Something very expensive
Hit the sack
Go to bed
The final straw
End of someone's patience
To be over the moon
Very happy
Take it with a pinch of salt
Not completely believing something you're told
Hang in there
Don't give up
Piece of cake
Something so easy (like this question)
To go to the dogs
Something that's become bad
Break a leg
Good luck
Let the cat out of the bag
Reveal a secret
On my larry
By myself
Spill the beans
Reveal the gossip or information