Well, being chased by a hippo while canoeing was exciting as was being chased by a Cape cobra (or whatever they’re called these days). Having our tent ripped to shreds by a black bear would have been harrowing except we weren’t actually in the tent at the time so it was just really annoying. The time that we were working up the Linyanti and the local guys I was with refused to put up a tent and insisted that we just sleep on straw mats around the fire because it was the dry season and malaria wouldn’t be an issue got interesting when what sounded like three lions started calling back and forth. At least that persuaded everybody to take turns keeping the fire going and sitting up with a .375 round chambered. About an hour into the first watch a young bull Cape buffalo charged through the camp, presumably to get away from the lions. Invigorating stuff.
My most harrowing experience with organisms, by a wide margin, was the second time I got malaria. Plasmodium falciparum and a mosquito (presumably Anopheles sp.) had me so sick that the technicians who were assigned to take me to hospital thought I had died. At the point where I was still conscious but not very coherent I desperately needed to go to the latrine but was afraid to move because I knew I’d vomit. That mattress had to be thrown out. So, yes, harrowing.