No, it doesn't hurt, until the moment of death . And what the human brain feels when it dies after cardiac arrest is difficult to say. Maybe nothing but maybe hellish pain. We will find out everything in due time.
To begin with, euthanasia in the Russian Federation is not permitted by law. At the same time, medicines and medical equipment for its implementation can be purchased without much difficulty. A triad of drugs used for the death penalty in the United States: sodium thiopental, potassium chloride, long-acting muscle relaxant. This same triad of drugs is quite suitable for euthanasia. The method is as follows, first thiopental, which knocks out consciousness, then muscle relaxants so that a person does not twitch, then potassium chloride. All this is done intravenously using a special pump.