keep one's head

1. Stay calm, retain self-control, as in When the rowboat capsized, George yelled that everyone should keep their head and hold onto the boat . This usage dates from the early 1600s and is about two centuries older than the antonym, lose one's head , meaning “to become confused and agitated,” as in Whenever the stock market goes down sharply, people seem to lose their heads and sell .

2. keep one's head above water . See head above water .