It's a nightmare induced by sleep paralysis demons. They attacked our camp in the forest. I guess they trap people in their dreams.

[He hesitantly puts a hand on his sword hilt.]

If you really can't push through, then I may have to kill us both.

[Or perhaps only Emet-Selch, given that it's his dream, but he doesn't want to tell him that. This poor man has gone through enough; Hijikata wants to give him assurance that he'll stick with him until they both come back out on the other side.]