Well as the Lily quoted the Will....
"Aziraphael, Aziraphael, wherefore art thou Aziraphael. For a book in any other cover would read so well.."
Besides, whyever would I need a potion to sleep? And, believe me, if Aziraphale tried to stab himself, he would most likely miss.
NEIL GAIMAN I AM SO SCARED THAT GOOD OMENS WON'T END HAPPILY☹️
It won't. It will have a very tragic ending. Crowley takes a sleeping potion, but Aziraphale thinks Crowley is dead and plunges a dagger deeply into his fair breast. Crowley wakes and, finding Aziraphale dead, becomes, in his heartbreak, a furniture delivery person and is crushed to death by a falling wardrobe. Then everybody cries.