Yuki has severe C-PTSD and is prone to night terrors. Though he normally dissociates once he wakes, eventually being able to resurface, when faced with a night terror regarding Tokumei ( a drug Isen used to inflict cruel punishment/experimentation on Yuki as a teenager ), he loses touch with reality immediately upon waking.
These night terrors are relatively rare, but they will cause Yuki to panic, especially if someone else is in the room with him. He’ll feel the walls closing in and, if the person with him is familiar and benevolent, he’ll beg them for something, though it’s often unclear what; normally a mix of ‘make it stop’ and ‘I can’t be here.’ It’s not uncommon for him to try and escape the room altogether.
Touching Yuki during these episodes should be done with extreme caution, as anything sudden will read as an attack, though sometimes it is unavoidable in order to keep Yuki from leaving or worse. But not to worry, he’ll come back… eventually.