This happened to me immediately after crafting a splint, while standing on a second-floor catwalk in one of those industrial-like warehouses. I wasn't injured at the time, just crafting a spare. No zombies or other players around. The screen flashed as though I was suddenly hurt, but I didn't lose any health. Autumn hunter pants ruined, as well as the FNX45 in them :(

Mouse sensitivity on the x-axis appears to be doubled when the player is in contact with certain kinds of geometry. I often fail to make the turn around staircase railings, because my character does a fast 180.