Aye, there are ethical issues involved in testing it! And your concern about predicting impending death is valid.
Having said that, I've come off my motorbike a couple of times, not at high speed but fast enough (about 40mph) without protective gear on (apart from helmet and gloves). I've not broken any bones (that I'm aware of). There's definitely something that kicks in that takes away fear, panic and pain as you're hurtling* through the air and skiting along the ground, but I think it's adrenaline, not DMT!
* I haven't really done much hurtling, it's mostly been skiting.