"Up sprang" is an idiomatic expression that means "suddenly arose" or "jumped up". There are several synonyms for this phrase that can add variety and depth to your writing. Alternatives could be "leaped up", "bounded forth", "vaulted up", "rocketed to his feet", "jumped to his or her toes", "sprung to life", or "jolted awake". Depending on the context, other suitable synonyms could include "surged upward", "shimmied up", "shot up", "catapulted" or "launched skyward". Choosing the most effective synonym can improve the flow of your writing and engage your readers with vivid and descriptive language.