I went out yesterday for the whole day, travelled by train at cab in the city. After the whole day at night, I got severe headache towards the back. I slept for 9 hours after that, had lots of water and juices. But, still the pain continues till now. I slept for more 4 hours in the day time. But, no relief. Should I take pain killer now? I usually don't prefer as i'm a bit habitual to headaches due to migraine. Is it because of the scorching heat out here? I just want to know the cause and how to get relief from it.