It's not the camera-movement when momentum starts, it's the lerp back into position once character-movement has stopped. I can reproducibly make myself slightly nauseous just by moving to the right just a bit, letting the camera slowly center, move to the left just a bit, allow the camera to slowly center, (repeat 10 times).
Locking the camera to the character would certainly solve it, but I wonder if there is also a way to implement the lerp back to resting-position that would take care of the problem. I don't know.