Dying alone
Darkness
"Everything" (For some reason I'm always walking around feeling like I'm about to get brutally murdered or something if I let my guard down. So I'm almost always on edge, and that usually causes my neck and shoulders to be tense, and that in turn causes headaches. I'm also ridiculously jumpy, which is pretty evident when some randomly and unexpectedly jogs up behind and past me when I'm outside >_>)