情不自禁的英语表达是 "involuntarily"。这个词来源于拉丁语 "involuntarius"，意思是 "无意识的"、"不由自主的"。

下面是一些例句：

She involuntarily flinched when he yelled at her.

He involuntarily tightened his grip on the steering wheel when he saw the other car swerve into his lane.

She involuntarily held her breath as she waited for the results of the test.