The phrase "big rush" can be used to describe a sudden burst of energy or activity. However, there are several other synonyms that can be used to convey similar meanings. Words such as "whirlwind," "frenzy," and "hurry" can all be used to describe a big rush situation. Another synonym, "stampede," suggests a feeling of chaotic movement or urgency. Meanwhile, "burst" or "outburst" may be used to describe a sudden or explosive surge of activity or emotion. Regardless of the specific word used, all synonyms for "big rush" suggest a surge or explosion of energy or activity that is abrupt and intense.