maybe you had loss of power or touched a circuit breaker by mistake. Its funny you would say tgis because I just finished wavehoppers campaign intro flying at 16,000 ft above a soup and my engine icing warning came to life. Shortly after starting anti icing by pedestal near fuel pump, my speedometer froze to 160 knots and upon descending in a nose down attitude, it turned all the way back to zero knots while I was flying forward in a dive towards base leg, and from thereafter, remained at zero knots. I used my surroundings till I came to hover then set her down nice and gentle.
The idea is that it could be electrical system freezing or battery problem.