I've tried to describe the Jain ritual of Sallekhana, which is fasting to death. The vow of sallekhana is taken when one feels that one's life has served its purpose; when one has no wishes/ambition/desires left, and no responsibilities remaining in life. It is also allowed in cases of terminal disease or great disability. The purpose is to purge old karmas and prevent the creation of new ones. If you want to know more about it, you may read 'The Nun's Tale' in a book called 'Nine Lives' by William Dalrymple. You may also see the wikipedia page on Sallekhana. Here's the link- http://en.wikipedia.org/wiki/Sallekhana.
Sallekhana is not suicide.
Sallekhana can never be
a violent reckless freefalling
plunge into that self-destructive
hellward spiral born of despair.
Yes, Sallekhana is a fast
unto death, but is death the End?
Isn't the human body a mere
vehicle that takes the soul on
its journey towards the greatest Truth?
Can one life ever be enough
to know all there is to know?
For the body is an object
that will slowly come to ruin.
One day it will fail to serve you.
Death by Sallekhana is just
like phasing out an old car as
lovingly and gently as one
weans a babe off the Mother's breast.