When people get very, very old or when they become extremely sick, their bodies can stop working the way they used to. This can cause them to feel very uncomfortable or even hurt a lot.
Some people don't want to feel this way, especially if there is no way to get better. So they might decide that they want to stop trying to make their body work, and instead let their body rest forever. This is called "dying by their own decision".
But it's important to know that this is a very serious decision, and not everyone is allowed to make it. Only people who are old enough and who fully understand what they are doing are able to make this choice. Doctors and nurses will also make sure the person is not making the decision because they are feeling very sad or confused.
Finally, just because someone decides to die this way doesn't mean they are bad or wrong. Sometimes it can be the best choice for them, so that they can stop feeling hurt and finally be at peace.