Unknown's Last resort

Unknown's Last Resort: So it's come this your last spell or should I say your last Trump card. Unknown's Last resort is an Enchantment spell that can one shot ANY CREATURE! However there is one flaw of this spell. no matter the hit points the Player's Character is instantly Killed along with the creature you used the spell one. once this spell is cast its effects cannot be undone nor Countered. not even 9th level spells can stop this spell from being cast since this spell is using the literal life force of the user to deal one devastating attack.It doesn't matter what level you do this spell at the effects are still the same. There is one exception however if your DM feels like they want to  they can save your life by having you flip a coin heads or tails one side will bring you close to death where your allies must heal you and you can't do any saving throws; The other side instantly kills you.