Okay, I fear this is veering alarmingly close to Bond territory, but I was wondering if there was a substance (or some other method) a person could use to make themselves appear dead, even to machines like a heart monitor, but so that they will either wake up later on their own or that they can be revived with one drug/method or another after having been "dead" at least long enough to be pronounced? The idea being that a person is captured, but, facing torture, they take the substance, and essentially kick the bucket (or at the very least it looks very much like it to the observers), but either wake up later or can be revived by those who know what they did/took. If no such substance exists, what about potential future substances? Or is this scenario even plausible? Or do the brains get permanently damaged if the person is dead to heart monitors and people trying their pulse for at least a few minutes if not hours? Is there any even borderline explainable way to make this work, or is it something that will always (for all intents and purposes) be pure fantasy? Thanks in advance!