What Causes Dizziness,pounding Around Neck And Head?

Hi, my mother is taking HTN meds. Recently she has been complaining of dizziness, pounding around neck and head, darkness when she lies down. this has been going on for a week. few days ago when she lied down, she complained of dizziness and as i gave my hand to help her stand up she fell down on the floor and hit her head. however, her symptoms dint worsen or disappear. i have no idea what to do or what it is?