The term "doubled up" typically refers to a physical pose or condition in which someone is bent over or doubled over due to pain, laughter, or other reasons. The antonyms for this term would be "standing straight," "sitting tall," or "lying flat." These phrases connote an upright and erect position, without any bending or folding of the body. Other antonyms for "doubled up" could include "relaxed," "calm," or "at ease," which refer to a state of comfortable and stable posture, with no discomfort or distress. By understanding these antonyms, one can better comprehend the various positions and states of the body, and learn to adopt the most appropriate posture for any given situation.