Fear
Bill Bryson, in A Walk in the Woods, captures this feeling of terror:
My particular dread--the vivid possibility that left me staring at tree shadows on the bedroom ceiling night after night--was having to lie in a small tent, alone in an inky wilderness listening to a foraging bear outside and wondering what its intentions were. I was especially riveted by an amateur photograph in Herrero's book, taken late at night by a camper with a flash at a campground out West. The photograph caught four black bears as they puzzled over a suspended food bag. The bears were clearly startled but not remotely alarmed by the flash. It was not the size or the demeanor of the bears that troubled me--they looked almost comically unaggressive, like four guys who had gotten a Frisbee caught up a tree--but their numbers. Up to that moment it had not occurred to me that bears might prowl in parties. What on earth would I do if four bears came into my camp? Why, I would die, of course. Literally shit myself lifeless. I would blow my sphincter out my backside like one of those unrolling paper streamers you get at children's parties (I daresay it would even give a merry toot) and bleed to a messy death in my sleeping bag.
Our situation was not that bad--while sitting in scared silence and straining to detect the animal's movements, I thought I heard some hoof-life steps. So, worst case, this was a prematurely rutting bull elk with the tattered and bloody remains our fellow campers' Gore-Tex apparel caught in his large and pointy rack. (I must admit that in my haze of fear I briefly thought that Satan is sometimes depicted as a hooved satyr, even though I knew that this idea was as cuckoo as me praying to almighty God for mercy and/or deliverance from this hellish predicament.)
After locating the bear spray, opening a hole in the fly big enough for peering, and listening to the animal crackling through branches behind us, we eventually determined that our companion was, in fact, a deer. It was large, and brave enough to walk right up to the tent, but still a herbivore. Despite the relief, we slept on pins the rest of the night.
In hindsight, there are few things as invigorating as being scared shitless. (Although I'm immensely grateful that the situation didn't require much courage, which is considerably more difficult to motivate.)

