Many things can trigger headaches. Some common headache causes include: muscle tension, caffeine withdrawal, sinusitis (congestion),  lack of sleep, constipation, spinal misalignment, food and seasonal allergies, as well as many other factors.

Most commonly, neck muscles that are tense, will cause headaches after you are under stress, sitting for long periods of time, bad posture, or in a high-impact incident that would jolt the neck (i.e. car accident).

Know of any other headache causes? Please post them in the comments section!