Causes: Since a tension headache is so common, the causes are pretty widespread. They're caused by anxiety, eye strain, caffeine, food, poor rest, bad posture, stress, hunger, or just about anything else you change in your daily schedule. Tension headaches are also usually the type of headache you end up with after a night of alcohol. Essentially, if something is abnormal about your day, whether it's a late lunch or a series of deadlines at work, a tension headache might pop up.