I have experienced plenty of migraines since my teens and I think I only just found my trigger which is dehydration. Wouldnt wish a full migraine on anyone, tunnel vision and vomiting, severe pain are the worst symptoms.
I have not experienced any headaches during my lifts though.
Hows your breathing? I could imagine that holding your breath and exerting stresses onto your body during the press would increase the pressure inside you which may be a trigger?