In most religions, suicide is either a sin or is not supported.The Catholic Church holds life to be sacred and suicide a sin, casting the soul into Hell. This proscription still holds true despite religious belief declining across the Western world. How many people linger in a coma while their relatives hope they'll recover?
e.g. Buddhism does not advocate suicide. Those following Judaism will be buried in a separate part of the cemetery.
But Christianity sometimes accepts suicide, e.g. the wicked falling on their sword. But in general a suicide is considered in negative terms.
In Islam. Hinduism, and Catholicism, as you said, it is considered a mortal sin.