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Pain in half head or hemicrania
can happen if you have stress physical/mental; it can be migraine
or tension induced headache.But since you are 40 yrs it is better to get your BP checked to rule out hypertension
.Please visit a doctor & get examined ;if the BP is normal he will advise treatment for headache.As for the weakness in arms it can be due to cervical spondylosis
so tell the doctor to check it.