沉住气

Literally 'sink-hold the breath' — picture pressing your panic down into your chest and holding steady. Imperative form (沉住气！) is a frequent line of advice/encouragement when someone is about to lose composure. Compare with 冷静 (lěngjìng, calm) which is more abstract; 沉住气 is more visceral and athletic.

memory

沉 (sink) + 住 (resultative: hold in place) + 气 (breath / qi). The 住 here works like English 'hold' — see also 记住 (remember-hold = remember), 站住 (stand-hold = stand still).