“情绪不稳定”常见的英文表达有：
emotionally unstable：这是最直接、常用的表达方式，清晰地传达出情绪方面缺乏稳定性的意思。例如：He has been emotionally unstable since the breakup.（分手后，他一直情绪不稳定。）
have mood swings：强调情绪在短时间内快速、大幅度的波动变化。例如：She tends to have mood swings, which makes it hard for others to understand her.（她情绪容易波动，这让别人很难理解她。 ）