一、in low spirits沮丧地；不振；意气沮丧；精神沮丧
Finding her in low spirits, they had persuaded her to join them for lunch.
他们发现她情绪低落, 便劝说她同他们一块儿吃午饭.
来自《简明英汉词典》
2. During breakfast those disembarking were in low spirits. 吃早饭时,今天下船的那几位都垂头丧气.
来自汉英文学 - 围城
in high spirits
兴高采烈；起劲；心情欢畅；带劲
At supper, everyone was in high spirits.
晚餐时，每个人都兴致勃勃。
来自柯林斯例句
二、spirit表示“某种精神”或“精神实质”时,是可数名词。所以in low spirits最好加上s。