Hunters suffered insomnia at far higher rates than the other two classes. It was common knowledge.
It wasn't just a product of nightmares of stress, like one would assume. All Guardians were given enhancements by their Light; strength, endurance, and they could take hits that would kill or maim a normal person. For Titans, the benefits to strength and durability were twofold, and the Light gave them a physically denser skeletal structure to make up for it. Warlocks had a greater sense of their Light, could 'think faster' than normal people, and occasionally has psychic tendencies, like Ikora.
Hunters had heightened senses, all five dialed to an eleven, sharpened instincts, and faster reflexes. It was those first two that caused the insomnia. Out in the wilds, where you could hear ever scratch of claws on dirt, every leaf the wind dragged across the ground, every predator loping past on a hunt of it's own, their overactive senses and instincts often pulled them to wakefulness for no reason, and kept them on alert when they needn't be.
It was the reason Crow took sleep aids when he wasn't in the feild. It was one of the reasons he often only slept an hour at a time.
It was what woke him and Cayde up in the dead of night, both their instincts screaming 'danger'.
Crow's eyes snapped open as goose flesh crawled along his skin. He blinked twice as his eyes adjusted, and a pair of unnatural white eyes blinked back from across their shelter. Glint stirred, lifting into the air slightly, but neither Hunter moved. They lay still, listening. In the dark, he saw Cayde's hand drift slowly to his gun.
Something crashes through the roots they were hiding under with an otherworldly screech, sharp splinters striking Crow's face as he jumps into action, darting out from the confines space. It's no safer outside; he immediately has to dodge the grasping hand of a Tormentor, and he's lost sight of Cayde.
"Scatter!" But he can still hear the exo. So he runs, dropping a grenade behind him for good measure. Screaming and bullet fire hound him, a round even hits his lower back, spreading a burning numbness. But he can still run, so he does, back along the many trails Cayde had shown him, until he's certain he's lost them.
Eventually, he makes it to another hiding spot, one they had designated as a 'shit went south' rendezvous point. There's no sign of Cayde yet, and he sighs as he sits down, tired and trying to convince himself the Ghostless exo would be fine.
Glint heals his injuries, and he pats his Ghost thankfully. At least they could have a spell of privacy to talk about this mess. Silver linings, Amanda would say.
Silver linings.