From personal experience, I thought this was possible only with ketamine or cocaine.
Sniff through one nostril; make half of the brain asleep while the other half remains conscious.
But now that I think of it; autonomous system shutdown ? I think you mean consciousness shutdown, if the autonomous were to shutdown, you'd stop breathing.
But, whatever the substance, I think the autonomous goes in hyper-drive rather than down. When the adrenaline kicks in (as it does in most out of body experiences), everything sorts of accelerates. The autonomous system is what regulates our body automatically. You can loose track of your breathing, forget your body and all, but I think it's the consciousness that slips away from your body. Also, in medical terms; the autonomous is more synonym with hormone regulation than breathing or heart beating. So I'm wondering if you don't mean something else than the autonomous system ?
But yeah ! Definitely, if your body shuts down, I'm convinced any decent entity noticing that happening will bring you back home. But maybe that depends on where you roam... ?