When I'm feeling moody, I sometimes think that no human is sentient by themselves: we are only sentient (conscious?) as a group; and, specifically, as a group we're "supersentient" with a shared "IQ" in the hundreds, or higher. When you're alone, your sentience (and consciousness) will continue on residually — perhaps decaying over time; possibly for the remainder of your life, but you stop being truly sentient.