From time to time during physical exertion, the back of the head hurts very much and there is pressure in the head. It has been going on for a week now, what could it be?

I agree with the previous speaker, most likely it's a matter of pressure, because being a hypotonic person (a person with low blood pressure) often felt the same. Measure the pressure, someone from your family probably knows the good old wheels that will ease your torment (with a low citramone, it helps me personally)

But again, we are sofa specialists, so the best solution is to go to a therapist for a referral to to the specialist

All the best, do not get sick 🍀

Not enough data to be sure. However, the symptoms indicate a syndrome of increased intracranial pressure, which occurs in various diseases: from hypertension (most often) to oncological diseases of the brain (less often). Here it would be to clarify the patient's age, concomitant diseases (if any), to measure blood pressure and pulse for a start. Then you can do additional laboratory and instrumental studies to clarify the diagnosis.

Py.sy. In short, do not guess what it is, just go to the doctor. Self-medication is not so safe.