The word 躺下 is formed by combining 躺, meaning 'to lie down', with 下, meaning 'down'. The character 躺 is a phono-semantic compound consisting of the semantic radical 身 (body) and the phonetic component 尚. 下 is a pictographic character originally depicting something below. In this combination, 下 acts as a directional complement to 躺, creating a verb phrase that explicitly denotes the action of lying down.