Silver says that his drowsiness hits him “hard and fast” and that it has been this way since he was a child, sometimes when he is walking, in the middle of a conversation, or doing sword training.
Silver says that he gets plenty of sleep at night and has no idea what it happens, and neither do any of the medical mages that Lilia has taken him to in search of an answer.
Silver seems to have come to the conclusion “it must be (his) laziness that makes (him) so drowsy”: when he falls asleep while training with a sword he decides “it must be evidence of how lax (he has) become,” and he tells his equally sleepy tsum that they both need more training.
We see a flashback from Silver’s childhood where he is sleeping while “standing up with a wooden sword in his hand” for his first introduction to Sebek, and another where Sebek chides him for “lazing about” in Malleus’ presence (Silver had fallen asleep).
In a chat Sebek accuses him of laziness as well, saying that “It’s not as if you’ve been enchanted by a fairy. You’re just lazy!”
There are many instances of Silver falling asleep throughout the game: in the woods behind the school, in classrooms, at the Halloween party, in the school courtyard, during his own birthday party, and more.
Silver says he has received “lots of bedding-related gifts” for his birthday as a result (“You wouldn’t believe how much I’ve learned about pillow types.”)
We also see him use Sebek as a pillow after falling asleep on his feet in a hallway, and while in line for the school store. He also falls asleep inside of the school store.
Kalim says that Silver also fell asleep during their art class while modeling for him, we also see him fall asleep during Vargas Camp when he is supposed to be guarding the fire.
Prior to Beanfest Ortho calculates that there was “at least an eighty percent chance” of Silver falling asleep during the event.
Twisted Wonderland Reference Note 