It's a way of describing that light-headed feeling you get when you are sick or injured or in shock. "Swam" gives you the image of your head floating around, not attached to your body, which is the way it feels sometimes.
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.
A hot head is someone who loses control of their anger easily.
"Dive in head first" is to rush into a situation without thinking.
He swam in the sea of diamonds
To turn completely around and head back in the direction you came from.
Keep an idea in ones head to act on it later.
That means you reacted to something negative without thinking first.
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.
SWAM is the past tense of the verb "to swim". For example, "I swam ten laps of the pool this morning".