Coming out of lurk for this one. Haven't been in the water for a while but one of the last times I was, a few years back, was in a heavy fog in northern Oregon. Too foggy to see the lineup, but could see surfers at the tail end of their rides, barely. Could hear the occasional yelp of joy from the surfers out there so I decided to go in.
The paddle out is low key in a channel once you get to it but the entry into the water is always intense because it's a rocky point break and bad timing gets you pounded back into the rocks. Usually I have no problems getting past it (except for the fear!) by just jumping out in between sets, but it was impossible to see sets coming in the fog. Got lucky though and got out with no problem (except for the fear).
Turns out it was well overhead conditions which at this spot is always intense because the waves are always thick and powerful (if a tad slow), not to mention the small room for error because of the rocky point. Very cool and exciting trying to judge waves approaching with the lower visibility. I think I managed to get a decent ride or two, but after one of them I was caught inside, somehow let loose my board during a duckdive and the wave broke my leash.
Fortunately I was bodyboarding and still had my fins,

but it was quite a rush being in virtual aloneness in the fog, no shore visible, not being in very good physical condition, trying to get back in via the channel riptiding out. It turned out to be not that big a deal (except for the fear), floated on my back, kicking, so I could see the waves coming while heading for shore, got back in okay, located my board which was undamaged and lived to remember it.
Not exactly a positive experience as surfing experiences go, but exciting and something I think about to tide me over until I get back in the water.
Happy surfing,