Hair
Khan could remain lucid during his nightmares, but his thoughts failed to enter the scenes triggered by his interaction with the Nak's hand. Only his consciousness reached the memories of the Second Impact.
The fire, the corpses, the smoke, the crumbling buildings, and the scorching crater didn't fill Khan with the usual desperation. He was still watching everything from his perspective, but a sense of peace invaded his mind.
That peace was odd, almost inhumane, and a coldness that didn't allow the presence of other emotions soon joined that sensation. Understanding dawned upon Khan at that point, and he hated to be unable to feel disgusted.
Khan couldn't think, but his mind still worked, so he could connect the dots. He knew where that inhumane coldness came from. He shared the same mental space as the Nak's hand, so he could experience its perspective.