My dad told me about geese once. About how they sleep. They work as a unit, regardless of how big or small that unit is. They sleep in a circle with one eye closed, the other eye — the one facing away from the center of their circle, remains open. The eye facing inside the circle, and it's affiliated side of the brain, sleeps first. The other side remains alert and aware of potential danger.
Halfway through the night, the geese do an "about face." They spin 180 degrees and allow the other side of the brain to sleep and the rested brain to take its turn at watch.
At one point humans had that capability, or so my dad said. But we evolved, and based on our position at the top of the food chain no longer needed that skill.
I've never wanted to de-evolve so badly in my life. That human trait would be a great asset these days—I'd trade in every electronic I had to be able to keep one eye open while I slept. We aren't sure where these things came from. Speculation cites space, Russia, China, hell, people are even throwing Big Pharma out there. I don't really care where they came from; only that they are here.
And we are not equipped to survive the onslaught of terror they have begun.