Double over is a phrase that refers to the action of bending forward in pain or laughter. Antonyms for this phrase include standing upright, sitting up straight, or maintaining a relaxed posture. Alternatively, you could use words that indicate the opposite emotion such as smiling, chuckling, or feeling amused. Similarly, you might use contrasting terms that suggest vitality, strength, or robustness rather than weakness or vulnerability. Ultimately, the choice of antonyms will depend on the context and tone of the sentence in which "double over" appears. Whatever antonyms you choose, it's important to use appropriate words that convey the intended meaning accurately.