He panicked the moment he heard the boss was coming.
Tips
usage
应 here is fourth tone ('respond to'), not yīng. Formally used in medicine and psychology; recently 应激 has become internet slang as a verb meaning 'to have a panic reaction, to freak out' — e.g. 我听到这个消息就应激了.
mistakes
Learners often say 压力反应 (stress reaction) by direct calque. That's understandable but 应激反应 is the actual clinical term.
