He'd been mostly speaking to himself in feverish worry, so being asked for clarification gives him a pause. He look up at Papyrus, trying to focus - its a good thing that skeletons don't need to breathe, or he'd by hyperventilating right now. The surges of magical energy in his body are being distracting in a similar way.

"There was a vampire," he says, trying to piece together his thoughts quickly enough to articulate them. "She got into my head - I couldn't stop myself."

With all the things he'd lost in his life, bodily autonomy was one of the few things he felt as if he'd maintained control over. He was unappealing, he was fragile, but his body was his and he'd had some degree of power over it.

In hell, he'd lost that completely.