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."
The head person.
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.
To turn completely around and head back in the direction you came from.
Keep an idea in ones head to act on it later.
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.
A very severe headache, as if an imaginary axe is "splitting your head in two".
"Your head is going to explode" IS an idiom. It means you have too much to think about.
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.
"Head over heels in love" would be one idiom.
That means answering with the first thought(s) that come(s) to mind.