Hello and thank you for using HCM.I carefully read your question and I understand your concern.You shoud not worry I ll try to explain you something and give you my opinion. A hypertensive crisis can give symtoms like headache, blurred vision, dizziness, nausea. A person might experience a kind of head reeling but it is not related with head position. In my opinion this symptoms like head reeling, vertigo, strongly related to head position or while lying down have to do with inner ear problem. In inner ear patologyes the patient experience this head reeling, like the house or bad comes over or up side down. They are strongly related with head movement and position becouse in that moment the inner ear takes imupses and controls our eculibre. So, my opinion is that your mother should consult an otorin and a neurologist doctor. There are some simple objective examinations to do and evaluate this problem. But you should not worry.If it is what I suppose there are medications to control this symtoms. Hope I was helpful.Wish your mother good health. Best regards.