Self-inflicted.
Northern Ireland, Jan or Feb 1997. 0300 call out, filthy weather (heavy rain and very low cloud). Low level (perhaps 250ft?), NVG, I was map reading, no GPS (see other thread!) black pen with a little red torch, co-pilot handling. Rad Alt set at 50'. Suddenly get "Can't see anything Sir, you have control". Ah.
Then radalt starts squawking.
Map gets chucked in the back, grab controls, aircraft already level but with a rate of descent, pull pitch into IMC and try to figure out what's happening. Bit quiet for a few seconds, then call Aldergrove and get an approach back home.
We'll never know how close we came...