Many years ago I had a pitot heater failure during descent (on a turboprop). It was a sunny day with barely a cloud in the sky. Except, We had to pass through a thin and wispy layer over our destination. It was barely 50' thick and I could see the ground through it.
The instant we entered it my airspeed needle wound around hard right, twitched, then dropped back to stall speed and shot back up again. The second we exited the layer it returned to normal.
Now, even though I knew exactly what was happening, and even though I was (for all intents) VMC, the sheer disorientating shock of that rocketing airspeed was unbelievable. It took every fibre of my will to not react instinctively to what it was doing.
On a dark and stormy night it would have been much harder.
I'm not sure how you train for that kind of shock.