Why do I feel a severe headache and dizziness as soon as I enter the Sacred Mosque (Al-Haram Al-Makki) area?

What you are feeling might be a delusion from Satan, or an evil eye, or a touch from a jinn. You should perform ruqya on yourself using the prophetic incantations, and strive against your soul to rid yourself of this feeling. Trust that if you strive against your soul, enter the Haram, perform tawaf, pray, drink your fill of Zamzam water, and make abundant supplications, then what you are experiencing will depart from you, and you will feel comfort, by the permission of Allah.