Based on the context and the answer, generate a question. 

Context: Then the pain kicks in , usually on one side of my head in my temple . My migraines almost always occur during a period of relaxation immediately after a period of high stress . Normally they 're somewhere between 6 and 18 hours of excruciating pain , followed by a day of feeling like I ' ve been hit by a bus .

Answer:

Because their body is so tense .



What may be the reason why their body experiences migraines after stress ?