I know I'll be jinxing myself by saying this, but I've only had it happen once. No crash dive, just a simple test dive to see how far I could go before it got too scary. Somewhere below 200 meters I couldn't pull out of the dive at all, even after blowing ballast and issuing flank speed. Nose was up angle like Sailor Steve's and still the boat kept sinking.
'Tis a mystery to me. I've tried to re-create the dive time and again but have been able to surface even after sustaining hull damage below the 210 mark.
