You're welcome Dawnt33,
I would ask your doctor about a triptan medication, something that works quickly like Zomig Rapidmelts, Zomig Nasal Spray or Imitrex Nasal Spray. There might also be other ones out there that melt in your mouth or come in nasal sprays. I say that because then if the visual problem does come on and your out and can't drive home you can stop it quickly. You will probably find that it stops the pain quickly as well. Be careful about getting caught up in using too many over the counter medications.
Everyone's headaches are different. Though you may not suffer as badly as your father inlaw you still have a lot of the symptoms, sensitivity to light, visual changes, pain sometimes, sick sometimes. I have challenges with my blood pressure which make my headaches really bad when I don't have it controlled. It's possible your father inlaw could suffer more for a similar reason or for a totally different reason.
Coquitlam55 (aka Nicky)
"The world is full of suffering, it is also full of overcoming it." --Helen Keller
I try and remember this each day I have a headache that I'm not sure I can overcome.