Though she's a good deal smaller than him, Sam is under no illusions that her powers couldn't turn him to dust if she so chose and he hesitates accordingly. There seems little reason to lie to her though.

"My brother," he says with a shrug. "He was sick. Both times." That isn't entirely accurate, of course, and Sam is purposefully choosing to leave out quite a lot detail. "He got better, but uh... they were pretty close calls. Got a little too close to the other side of the veil."