I read this when I was in Jr. High (on the bus to school IIRC) so the story couldn't be any newer than 1982. Again, IIRC it was in a science fiction short story collection.
It's told from the first-person viewpoint about a group of soldiers fighting alien "snails". These creatures were telepathic and had the ability to induce what the humans called "snail fever" which was described as falling down a well (vertigo) forever. As I recall the story does not end well
The story may, or may not, have been also collected with the (in)famous Harlan Ellison story "I have no mouth and I must scream", but I cannot be certain of this.
Sorry for the indistinct memory and details; my memory is failing me and everything is suspect.