It means you have an itch.
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.
Just stretching out to get the really itchy spots.
Scratching is relieving an itch.
Do you mean scratching? It is normal for all cats to scratch: it is marking its' territory.
he has a habit of lightly scratching his head
She may have a skin condition, or a rash or some kind. You should take her to the vet.
Discipline my friend
If your head is "in the clouds," you're a dreamer.
This dog needs regular exersize. This will discontinue the nervous chewing and scratching.
To "keep you head" means to it means to "stay calm" and not to panic when faced with an emergency situation.
puzzled,the riddle left Jennifer scratching her head in confusion
Scratching a calendar