The best way to train unusual attitudes (in French "positions inusuelles") in IMC is VMC aerobatics once again. The big difference between IMC and VMC is the size of your horizon. The wide angle of the natural horizon helps to emphasize your understanding of the relative body/plane's position, and helping your eyes to grasp the horizon to recover your level position and feeling it too. It is the best training for the pilot student to fly later in IMC with the HSI with its much smaller horizon.
Why did the speed decrease since 01:40 from 280 KT to 220 KT at 01:44:30 at the beginning of the second (last) EPR anomaly episode , A/P throttle mode OFF at 01:45:08 after MCH EPR LIM ?
That was followed by the final oscillating LOC reaching 150 KT at 01:45:45 before wing/nose diving probably without stall's AOA, as Machinbird said, toward overspeed in roll and rudder fast oscillations.