This is pretty crazy. I have similar experiences specifically with the memorial site. Usually, I get headaches from spending too much time in the spiritual realm, which I didn't even know I was doing at first but if you are consciously thinking about your thoughts you are doing spiritual work. You might just naturally do the same which makes you more sensitive to spirits that linger in the physical. What I realized is that when something like this happens the headaches will start if I am closed off to receiving whatever emotions come with the experience. So its difficult but I try to just allow myself to feel the feelings no matter how intense. Hope this helped :)