The pattern where you become dizzy with tilting the head back is suspicious that you may be having some interuption of the posterior circulation to the brain.
are you suggesting a cervical spine issue?
The posterior part of the brain is supplied by vertebral arteries. If you have some arteriosclerosis(caused by high blood pressure) or atherosclerosis(caused by high cholesterol then the arteries are more stiff and more likely to occlude or partially occlude when they are bent.This bending occurs with bending the neck back. You might mention this to your docotr. It might not be anything serious but it would be worth checking the circulation system(carotid and vertebral arteries)
The MRI may be matched with an MRA of the neck and brain as one option to look in detail at this. On the other hand an ultrasound of the neck vessels may suffice...
(MRA =magnetic resonance angiogram)
I hope this information is helpful for you. If you have further questions then let me know and I will be happy to get back with you. If my answer has been helpful and to your satisfaction then please remember to press the "ACCEPT" button. Thank You and Best Regards,
Anthony Bray MD