In The Name of Allah, The Most Gracious, The Most Merciful
I had the same problem before. And b/c of the headache I used to get so discouraged about Salah. but Alhamdulilah, I'm making lots of Du'a to Allah, Az wa Jal, to grant me khusyu' in Salah. I don't have the headache problem anymore. I think its Shaytan trying to discourage us or keep us away from giving Allah His due rights. Don't give up brother, Insha'Allah, in time it will get better. It did for me. sincerely make Du'a and continue to struggle for Khusyu'.