Toki yo Kaere! Natsu no Hi(1975)

Toki yo Kaere! Natsu no Hi

A girl was almost late for school, and while the bell announced the debut of classes, she got hit by a car and ended up in the hospital in a coma.
A few years later, a nurse happened to bring a metal basin to his room, and he accidentally dropped it on the floor, and the sounds, similar to the school bell, wakes her up.