Thank you very much for the useful information Tessie.
Most common cause for such kind of headache is spasm of the muscles at back of neck and in the scalp. This is commonly referred to as "Tension Headache".
Off course stress contributes to it but there are other causes as well such as inadequate sleep, concurrent illness, anxiety, exposure to extremes of temperature etc.
Little increase in blood pressure can also give you the same symptoms.
And, problems with the eye sight can also present clinically with headache but this is usually accompanied by pain around the eye.
The best step right now is to take regular pain killers which include Ibuprofen (Motrin) along with Tylenol continuously for few days and see how you respond to it.
Also, have adequate rest.
Avoid prolonged sittings/work shifts.
Since there is no vomiting, weakness of any body part (which are serious symptoms and point towards a sinister cause for the headache), there is no need to panic. Just monitor your blood pressure and wait for another few days. Hopefully this will settle down soon, but in case if this does not improve, persist, get worse or if you get any of the warning symptoms (mentioned earlier), see your doctor for a more detailed evaluation discussing all the details i have mentioned to get a management plan chalked out that suits best to your needs.
Your doctor may order CT of the brain to make sure there is nothing seriously wrong which will also put your mind at ease.
Keep yourself adequately hydrated.
I would have been worried too if I were at your place, but let me reassure you that this does not sound serious at all. It is a treatable condition and carries a good prognosis with appropriate management.
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