The causes of tension headaches are not well understood except for one: “The only thing that clearly does trigger tension headaches is stress,” says Dr. Goadsby. Poor posture is another possible culprit. Holding your neck muscles in one position for too long -- hours or computer work, sleeping in an awkward position -- can also set off a tension headache. Other triggers may include a change in sleep patterns (too much, too little), low blood sugar from skipped meals, dehydration and jaw clenching or grinding. Some foods, such as aspartame, alcohol and caffeine, are also linked to tension headaches.