How do i no when to worry about a headache?

Headaches: The most serious headaches are: headaches associated with fever or injury, severe headaches, headaches unlike you have ever had before and headaches that seem to be worseinng in severity, intensity or duration over time.

Red flags...: Red flags or worrisome symptoms associated with headache are: fainting, loss of vision, leg or arm weakness, persistent vomiting, worsening of pain when bending over, new onset headache you have never experienced before that becomes very intense and more frequent.