Sometimes i get a sharp shooting pain in my head like a knife is stabbing me. it comes on suddenly and leaves very quickly. what could this be?

Headache syndrome: There is a headache syndrome that is associated with exactly what you describe. If persistent and new, you should be evaluated by a health care provider like a neurologist who is familiar with these syndromes. There are medications that can help alleviate the symptoms.

Headache: With this amount of information I cannot give you a definitive diagnosis. However it is probably muscle spasm and of no consequence