I've had thick fog set in on me twice while hunting and it was brutal.
Back before the fancy gps trackers a friend and I were hunting hogs on the river bottom with dogs. It was like 2am and the fog set in. We couldn't see 5' in front of us. I have a pretty good sense of direction but it got a little disorienting. We snapped the dogs up because there was not way we could get to them in a reasonable amount of time. We were trying to get out of the river pasture because it has big washouts in it. The grass is several feet high and it can be hairy in good light. The pastures didnt really have defined roads. You were trying to find random gates in fence lines with no references. We had about 3 miles to get back to the truck and it took a couple hours.
I was hunting in WTX and had a pop up tent on a mountain. It was an hour or so before day light. I pulled up to the tent on my buggy and dropped all my gear off. I pulled around on the back side of the mountain to hide the buddy which was only about 50yds. All I had was a little flashlight and my pistol. I got about half way between the buggy and the tent right on the peak and fog set in. It was like looking at a wall with my little light. I would walk out a little to where it started sloping and work my way around. I did it several times with no luck finding my tent. I felt really dumb. I sat on a rock on the peak in the pitch black dark for a minute to kind of think about it. All I could think to do was sit there until light. I walked on more time and walked right up on it and got in.