Just a glitch I imagine. I had something similar, but I was just standing still in the fire station at the airfield, then the screen goes grey as though I've taken damage. That goes away and I'm fine, but my trousers are ruined

It makes for the most confusing times I've ever been through in this game. I thought it was the broken leg glitch first until there was a 6 man free for all and all hell broke loose.