* * *
Humans were one of the relatively few species who rested their entire brain at once: closed both eyes and went fully unconscious. Many other animals only rested half their brain at a time, and slept with literally one eye open.

It felt to Cassian like he'd been sleeping with one eye open most of his life. Right now, with Jyn, for the first time in years, he went fully and deeply to sleep.

The down side to that was that it allowed him to dream.

on the broad steps to carida academy
the tall man crumpled and the boy ran out from cover
brandishing a toy blaster and uselessly trying to defend the man with it

he deposited a handful of grit into the gears
finding the right ones despite biting his lip to bloodiness
to not think about the terror of being inside the war machine
the moving parts that enclosed and could crush or maim him
he was small and slipped out again and cheered with the rest to see the machine explode
but in his dreams for the rest of his life, as he hadn't at the time
he saw the operators trapped inside burning alive
because of him

he fought so hard - whirling around and around himself - couldn't stop if he wanted to
and he did want to but
frightened at the momentum - at how it went on without his own consent - at how he was trapped in it and couldn't break out of it
until suddenly it was done - he was still - looking down at the bodies splayed out around him
and though they'd been stormtroopers a moment ago
now they were everyone he cared about and had been trying to protect

screaming at kay not to leave him alone

making love to jyn
suddenly her kyber pendant in his hand as he throttled her with the cord
his hand on a blaster firing into her stomach
her lips going black because he was poison
her body pregnant from him but it was blood and knives that tore her coming out
her going limp and face turning blue and he could do absolutely nothing

No wonder he never allowed himself to fully sleep. If he'd thrashed and screamed like this on assignment…