Feign Death (Necromancy) 3rd-level Wizardor 3rd-level Priest spell  Sphere: Necromantic  Range: Touch  Components: V, S (arcane) or V (divine)  Duration: 1 hour + 1 turn/level (arcane) or 1 hour + 1 round/level (divine)  Casting Time: 1 (arcane) or 1/2 (divine)  Area of Effect: Creature touched (arcane) or Person touched (divine)  Saving Throw: None 
 By means of this spell, the caster (or any other creature whose levels of experience or Hit Dice do not exceed the wizard's own level) can be put into a cataleptic state that is impossible to distinguish from [actual] death. Although the person [or creature] affected by the feign death spell can smell, hear, and know what is going on, no feeling or sight of any sort is possible. Thus any wounding or mistreatment of the body is not felt and no reaction occurs; damage is only 1/2 [one-half] normal. In addition, paralysis, poison , or energy-level drain cannot [does not] affect an individual [a person] under the influence of this spell. Poison injected or otherwise introduced into the body takes effect when the spell recipient is no longer under the influence of this spell, although a saving throw is permitted. [However, the spell offers no protection from certain death - being crushed under a landslide, etc. [...]]
Note that only a willing individual  can be affected by feign death. The spellcaster can end the spell effects at any time desired, as will a successful dispel , but a full round is required for bodily functions to begin again. [Note that, unlike the wizard version of this spell, only people can be affected, and that those of any level can be affected by the priest casting this spell.]
 Caveat: Two slightly different versions of this spell exist in AD&D, both of the same level.
 Ignore this entry.
 As written.
 Decide for yourself if you want the "S" component or not.
 Decide for yourself if you want a slightly longer duration or not. A "turn" is equal to 10 minutes.
 It's not unbalancing to decide to give the spell [in 3.5] a Casting Time of "one swift action". That was the intent of the divine version.
+ It would be a very restrictive decision to limit the "Target" to "One willing humanoid creature", but if that's your POW, go ahead.
 What about: "No, see text"?
 The text in parenthesis [ ] is the text from the priest version of the feign death spell.
 In 3.5 poison normally affects a creature only in the round it was conferred/introduced (in)to a creature's body, and 1 minute thereafter. It would be left to you if you want to make the feign death spell a poison inhibitor ["makes the creature immune to poison"] or to simply postpone the Fortitude saving throws ["the creature must make the Fortitude saving throws after the spell ends"].