How would you describe the feeling of anxiety (that wasn't triggered by any external factor)?

I sometimes wake up with a strange feeling that I can't name. I was thinking about something like "feeling the closeness of death" or "everything darkens, everything gets deep purple and shabby and completely devoid of happiness (silent hill movie setting is actually a very good visual depiction of that feeling).
Now I realized what else I could compare it to, even though I've never been in such situation - the feeling you get when you learn someone you loved died or that some great disaster happened. Your house exploded, the war was officially declared, your doctor told you that you are seriously ill... First seconds after you learn about it. That fright.

Can anyone relate?