The phrase "get off chest" refers to the act of expressing something that has been weighing heavily on one's mind or conscience. Antonyms for this phrase include "suppress," "conceal," "repress," and "bury." When one suppresses or conceals their thoughts or feelings, they may experience negative emotions such as anxiety, guilt, or resentment. Repressing or burying emotions can also lead to physical symptoms such as headaches or stomach problems. Therefore, it is important to find healthy ways to express oneself, such as through talking to a friend, writing in a journal, or seeking professional support.