"The latter, probably," Carlisle replies. "I mean not to get ahead of myself, but- but do you know how long it's been since I slept? Do you know how maddening it is to be awake all the time, constantly having to listen to your own thoughts, turning over every idea and notion a thousand times more than they ought to until they're just- they're just twisted and terrifying, even if the idea hadn't been frightening to begin with?"

That likely does explain some of the stress he's under, especially when that's all on top of his being-an-undead problem.