People instinctively want to keep their head out of water. In floatation tanks they give you ear wax to plug your ears, and the salt water is supposed to suppor

People instinctively want to keep their head out of water. In floatation tanks they give you ear wax to plug your ears, and the salt water is supposed to support the weight of your head, but basically only your face will stick out. So you might over compensate to prevent your eyes and nose from being submerged. Not sure if this works for everyone though, different shapes and sizes of head and neck.