It means that whatever symptoms you are experiencing, they are imaginary. The image is of whatever it is existing only inside your head and not in reality.
The idiom "it's all in your head" means that something is imagined or not real, and is only a product of one's thoughts or perceptions. It often implies that a person's fears or concerns are not grounded in reality.
The idiom "a hot head" refers to someone who is easily angered or quick to become upset or frustrated. It implies that the person has a tendency to react emotionally or impulsively in challenging situations.
Imagine that your head is a light bulb. If it is screwed on right, the bulb lights up. This idiom can mean either that you are a smart person or that you are a dumb one, depending on how you use it. Examples: He really has his head screwed on right. This means he is smart. He doesn't have his head screwed on right. This means he is dumb.
The idiom "you are such a brain" is typically used to compliment someone's intelligence or cleverness. It means that the person is very smart or sharp-minded.
"Weak in the head" is an informal idiom that means someone is not very intelligent or has poor judgment. It suggests that the person is not very mentally sharp or capable.
The idiom "to brain someone" is thought to have originated from the idea of using one's brain as a weapon to strike or hurt someone. It is a figurative expression that means to hit or strike someone on the head with great force.
The head person.
If your head is "in the clouds," you're a dreamer.
Stay calm
An idiom is something that does not mean what the phrase says literally, so yes. You can't actually laugh your head off.
"Dive in head first" is to rush into a situation without thinking.
It can mean different things according to the context. You should probably ask the person who said it what they meant in that case. Sometimes it can mean that the person is imagining something, as in "You're not really sick, it's all in your head."
It's not an idiom. It means exactly what it says. "By all means" or "by any method necessary."
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..."
Keep an idea in ones head to act on it later.
To turn completely around and head back in the direction you came from.
If used as an idiom, it usually means that you are confused about something. The image is of you scratching your head to try to think better.
It's not an idiom. It means just what it says - every generation in the future.