The antonyms for the phrase "am vertical" are "lying down," "sitting," or "kneeling." These expressions refer to different body positions in which an individual's body is not in a straight vertical position. Lying down means that the body is resting horizontally on a surface, such as a bed or a floor. Sitting involves placing your body on a chair, stool, or any other seat, keeping your back in a supported upright position. Kneeling means resting on one or both knees, often used in religious ceremonies or as a sign of respect.
Overall, the antonyms of "am vertical" describe various positions in which a person can be in, indicative of rest, relaxation, or distinct practices.