Hospital Massacre (1981)

When Susan was a little girl, she rejected the Valentine of a lovestruck classmate. Decades later, she’s come to the hospital for a routine medical examination, and finds herself trapped in a bizarre nightmare, made all the worse as her vengeful childhood valentine, disguised among the hospital staff, begins murdering everyone in his path as a means of proving his undying ‘romantic’ obsession…

Unfortunately the movie Hospital Massacre is not yet available on HBO Max.