It'd be like a microburst. Not so much the way the airmass moving fast is somehow different than the plane moving fast in a still airmass… more that it's a sudd

It'd be like a microburst. Not so much the way the airmass moving fast is somehow different than the plane moving fast in a still airmass… more that it's a sudden change IN the state of the plane in the airmass. If the air suddenly stopped moving past the plane, that doesn't mean the plane suddenly starts moving past the airmass (ignoring its own inertia relative to its position in the world) to make the same airspeed. Instead, if the airmass suddenly changes velocity, the plane stays in position, stalls, and drops like a rock. It's the rate of change that'd get ya: if it changed velocity very very slowly, you'd end up just zipping forward and not stalling at all. But the airmass suddenly reversing, that'd stall you immediately.