#1 R/o Dx HAS to be a SAH d/t ruptured berry aneurysm. If you miss this, patient dies.
Reasons:
Hx of Polycystic Kidney Dz
High BP + Not on BP meds
Neck Pain + TTP posteriorly without evidence of trauma
"Headaches intermittently, has not seen a neurologist. This headache is different."
DDx includes - TIA (FHx of CVA + Pt's BP), Vasovagal, situational syncope (as VT said), Maybe a tumor (idk if I would include that on an official list).
For practice, that's what you do. In real life someone would come in with syncope + head pain, get a head CT to r/o a bleed in the ED, then go on with rest of the workup.