Incoherent half asleep thought but what if Riku sometimes builds up like a residual charge of dream eateryness in the waking world which causes his subconscious to slip into the realm of sleep when he goes to sleep, but in a way more intense and literal way than when normal people dream because he’s a creature OF the realm and not just a visitor. So he ends up not getting any rest because he’s fighting random nightmares the whole time, which is especially bad since when regular people get hurt or die in a dream they just wake up, but he could actually wake up with physically manifested injuries or simply die in his sleep.
But then Sora figures out that since Riku is primarily HIS dream eater, he can pull him out by linking with him to quickly burn off the weird dream eater aura that’s keeping him stuck inside the realm of sleep where dream eaters are supposed to stay.
And it doesn’t happen super often, but better safe than sorry and Sora is a pretty deep sleeper so it’s probably just best if they share a bed and cuddle so Sora can feel it when Riku starts twitching like a dog dreaming about chasing stuff. Yup.