Here is an idle thought about the connection between the "sloshing sensation" and the trembling of the trapezius described in this article.

The accessory nerve (cranial nerve XI) innervates both the trapezius and the sternocleidomastoid.

Perhaps the original trauma drove the C1 vertebra forward, crushing the accessory nerve between the transverse process of the C1 vertebra and the styloid process.

Accessory nerve damage explains the trembling of the trapezius.

Accessory nerve damage could also explain the sloshing sensation. The sternocleidomastoid plays a major role in stabilizing the head.

Dysfunction of the sternocleidomastoid could create a feeling of wobbling or sloshing, particularly with head flexion or rotation.

What do you think?