If you save the poison is not in you. If you fail your save, the poison has entered your blood.
On the first round after failure, you take 1d6 damage. You are -1 on all actions. There is a 1 in 6 chance you fall prone, either unconscious or writhing around in agony (50/50 chance).
On the 2nd round after failure you take 2d6 damage, you're -2 to act and have a 2 in 6 chance of incapacitation.
On the 3rd round you take 3d6, -3 to act, 3 in 6 KO.
Etc., etc., up until 10 rounds have passed, when you take 3d6, -10 to act, 10 in 6 chance of incapacitation.The idea here is that being poisoned will kill almost any character in a few rounds, BUT you have some time to try to pull some shenanigans, like sucking the poison out or overcoming the hit point damage with cure spells and potions. And you get an opportunity to maybe kill the sumbitch who poisoned you, only to fall over dead a round or two later. How awesome is that?