There are various antonyms for the word "sate back," which means to relax or recline comfortably. Some opposite words for sate back are tense, upright, alert, agitated and nervous. If you contrast sate back with tense, it means that you are in a state of anxiety or worry. If you're upright, you're alert, ready to react or respond to any situation. Meanwhile, if you're agitated, you're restless and uneasy. Lastly, if you're nervous, you're tense because of anxiety or excitement. Therefore, while sate back conveys the act of relaxation, its antonyms demonstrate a state of tension, anxiety, alertness, agitation or excitement.