The phrase "was on back" means lying down, reclining or prone. Its antonyms include standing up, sitting, erect, and upright. These words imply a physical posture that is opposite to the state of lying down. They convey a sense of alertness, readiness, and engagement. For example, someone who was on their back may "stand up" to take action, "sit" to have a conversation, "erect" to express confidence, or "upright" to show respect. Knowing the antonyms of "was on back" can help us describe movements, gestures, and postures with more precision and clarity.