Interesting theory, but it doesn't work for me.

It says that he drank the draught of living death
all the way back in the cave and then, after:

conjuring the ring of fire and holding it there,
escaping the cave and the inferi,
the freezing swim,
the journey home,
conversations with Harry and Rosmerta,
flying on a broom,
de-activating all the magical protetections so they could return to Hogwarts,
putting the spell on Harry,
chatting with Draco and others,
Snape's curse,
the fall,

-- he managed to stay awake through all that,
and the potion didn't kick until hours later?
Doesn't seem likely.

Everybody and his grandmother has posted on how
he could have survived the avada kadavra curse --
he didn't. It was a fake. Snape used some other spell.
I can't think of the name of it, but I can look it up if you care.

How did he survive the fall? Paddawan, you said
you read my "Snape the Death Stopper" post.

And anyway, what neckalace?