I had a chemical stress test Wed. and I got a severe headache during the tread mill test. It was horrible. I never get headaches and this one was extreme. It took quite awhile for it to go away, but it did. However, I woke this morning and my headache came back and still have it almost 10 hrs. later. I ve taken Tylenol, but not helping so far. Could something have happened during the stress test? The nurses had me smile, checked my eyes and had me stick out my tongue. They were satisfied that I didn t have a stroke of some sort. But WHY am I having these headaches?