There are certain ways to kill the cognition while relaining alive - repetitive cycles of high-intensity ECT for example, however it won't let you find "the peace you had before your injury".
If you consider the state of deep, dreamless sleep to be "peaceful", most likely you will find the same, if not greater, peace in death. You will not be able to recognize it, as the cognition is dead, but similarly you don't recognize the peace and length of sleep, as cognition is deeply altered and deminished in favor of restorative neural processes, for example.
So death, most likely, is actually the truest peace, as long as you don't require luxuriating in the experience of peace,but are rather content with its complete presence.