This is definitely a real issue. I never get headaches. I've had an iPhone since the very first one came out. On Friday I noticed that I had an odd headache in the evening. I didn't think much of it. On Saturday evening it happened again. I again just thought it was nothing. Then on Sunday I got another headache in the evening. That's when I noticed it was a trend and that something was causing them. I thought of what could possibly be causing the headaches. I noticed they started exactly when I got the iPhone Xs Max, so I did a google search and here I am.
For those of you that got headaches with the iPhone X, did they go away after time. I like my new iPhone, but I cannot put up with daily headaches. If they continue, I'm going to need to return it.
BTW, headaches for me are extremely rare.