What does knotty-headed mean?

If you are referring to the movie Elf made in 2003, then the correct spelling is "Cotton Headed Ninny Mugger." I is basically an Elf that is bad at making toys or other elf qualities "I can't make...

A level-headed person is someone who remains calm is stressful situations, who doesn't panic but can think under pressure.

Someone exercising or showing good judgment.

It means that the 11 year old is dizzy and they should just relax and sit down.

Hard headed is a term used to signify a person who takes a lot of explanation and persuasion to make him understand something. It is also a term used to signify someone who is very stubborn.