It means to remain calm and rational in the middle of a chaotic or confusing situation.
The poem "If" by Rudyard Kipling begins: "If you can keep your head when all about you/ are losing theirs and blaming it on you..."
If your head is "in the clouds," you're a dreamer.
Stay calm
Keep an idea in ones head to act on it later.
The head person.
An idiom is something that does not mean what the phrase says literally, so yes. You can't actually laugh your head off.
This is not an idiom - it means exactly what it says. You should stay fit and healthy.
To keep struggling and not give up.
it means that
"Dive in head first" is to rush into a situation without thinking.
Keep bothering someone.
To turn completely around and head back in the direction you came from.
It means " keep calm, don't get worked up"