@machinist,
Please understand I am no doctor, and giving medical advice is against the Terms of Service anyway. I do know when my father was having these sorts of symptoms, he ended up getting carotid artery bypass surgery from, yes, a vascular surgeon. They did find blockages. It turned out my father had different issues (it's a sleep disorder with him, it turns out) but the vascular surgeon explained that with a lot of women who have strokes, it can happen in the shampoo chair at a salon. That is, they have blockages at the backs of their carotid arteries (e. g. in the neck), and the act of bending their heads back cuts off the small passageway they have left.
I am not saying you have this. Again, to clarify, this is not intended to be medical advice. It just seems that if you are having issues when your head is back, someone with knowledge of veins and arteries should probably be checking that area to see if you are at risk.