mercy killing

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my grandpa died in a hospital bcoz of sickness. Since then there's something bugging my mind. Before he died the doctor told us that if the pulse rate drop we have the option if we want them to revive him or not. Since my grandpa is so sick and maybe if they revive him he still in not good condition so we and other relatives decided not to revive him. Is that what you call mercy killing? are we really responsible for my grandpa's death?