She worked too long in the heat and suddenly fainted, experiencing a brief black-out.

black-out 是由 black（黑色）和 out（出去）组成的复合词，字面意思是"变黑"或"失去知觉"。在医学上指由于大脑供血不足导致的短暂意识丧失，即"昏厥"或"意识丧失"。