I want Grace to explain to Rocky what sleeping disorders are, because they must been a living nightmare for eridians, or just seem like a blant lie.
Like think how some of them would look for the eridians
Insonmia: Difficulty to sleep; for the eridians who they fall sleep, because hey can't fight the tiredness, not been able to sleep just seem imposible.
Sleep apnea: Breathing stops in the middle of your sleep; eridians would see this as terrifying, specially because for eridians who "breathing" doesn't work the same as humans that can see the chest inflating and deflating, eridians would not be able to see if a eridian stops "breathing".
Narcolepsy: Sleep attacks, getting sleep without any warning or as a stress response; The idea of been scare and then falling sleep in response to that fear, or just fall sleep without even been able to tell when, another eridian nightmare, too much vulnerability.
Hypersomnia: Feeling sleepy all day long; Feeling like your falling sleep but not falling sleep, and feel like you can't control your on body, other eridian nightmare.
Circadian Rhythm Disorders; Having troubles to tell when you are going to fall sleep or wake up; The one I think the eridians would related the most.
Parasomnias; Sleep walking, sleep terrors, sleep talking; all things that a eridinas, who are just... gone while they are sleeping can't not lik with sleeping, how can your body or mind be doing other things if you are just gone?
I also think that Grace should have one of this disorders, of course he already have insomnia, but I vote for including another (or multiple) parasomnia, because like I say these disorders are the ones that go the most against what sleep is for the eridians;
Sleepwalking; Rocky would watch Grace fall sleep just for him to stand up and keep walking through the spaceship, or the dome. It is unnatural to see Grace, who doesn't normally move with grace, move even more clumsy and still be snoring.
Sleep talking; Grace still rambling about science even in his dreams and Rocky thinking that even in his sleep Grace can't have a moment of peace.
Sleep terrors; Grace screaming and crying,and begging for his life just to fall still the next second, and Rocky can't do a thing to wake him up, and then when Grace wakes for himself he doesn't remember what he was dreaming about.
Rocky would be so concern, because it is bad to see your friends going to sleep and not moving, but seeing your friend fall sleep just to see pieces of him still been able to go beyond his inconscious state, specially if is his expressions of distress or panic, must be quite the experience.
Simon who knows about nightmares (of course he knows about nightmares, he survived a nightmare, multiple times), but didn't knew about the the other parasomnias, because it that information was lost through time and people who suffered from these parasominas keep it quiet in fear to be thought to be possessed, sick, or defective.
Simon who is a ligth sleeper waking up for Grace screaming as if he was been skinning him and saying "You are murdering me!". Simon rushing to get to to Grace to help him just to find him crying and when he is about to wake him up Grace calms and his face changes to the most calm expresion he had see in a sleepy face.
Simon waking up by Grace ramblings about explosions and predators, and science terms Simon had never heard before, or asking "who I am?" as a mantra in his sleep.
Simon watching Grace without any destination, taking tools from the lab and repeting in his dreams a process he had done multiple times.
Simon waking up to see Grace walking next to his bed with his eyes slighly open directed in his direction and murmuring non-senses "you are murdering me...I, I don't wanna die, maybe even crying quietly and disturbing Simon.
Simon thinking that Grace is a ghost of someone that he killed when fighting for Eden, maybe someone from Filament Station who died in the explosion.
Simon thinking that Grace has came to haunt him.
Simon thinking that Grace is been possesed by the people he had kill and he is paying for having help Simon survive the Blood Ocean.
Rocky and Simon been horrified by Grace sleeping.
Rocky and Simon trying to find a solution for Grace's parasomnias or to accomodate the spaceship or the dome so Grace doesn't get harm.