[BobK]

A few more, related to the head (again):

with your head in the clouds - oblivious to your surroundings:
"After seeing her for the first time, he spent days with his head in the clouds"

up to your ears in - engulfed:
"They were up to their ears in e-mails." (Note: 'up to your <whatever> in' is often not idiomatic, but just exaggerates: "I was up to my knees in mud".)

keep your head above water - struggle to stay on top of a situation:
"There was so much to do, it was all I could do to keep my head above water"

keep a stiff upper lip - not to show disappointment or fear:
"In any difficulties, a Boy Scout always keeps a stiff upper lip."

keep your chin up - be determined/unbroken
"However bad things look, keep your chin up." Often, in situations that might seem to call for the imperative, the verb is dropped altogether: "Chin up."

b