The following websites discuss the possibility of having a stroke when the person getting their hair washed bends their head backwards over a shampoo bowl.
The Comfort-Cape allows you to remain seated upright so you are not bending your head backwards over a shampoo bowl.
BBC News (December 2016)
Can a hair salon sink wash be a stroke risk?
Buzzfeed (March 2016)
People are Having Strokes at Hair Salons and This is Why
National Center for Biotechnology Information
National Library of Medicine (March 2000)
Cervical vertigo after hair shampoo treatment at a hair dressing salon: a case report