"Era să cad!"
Translation:I was about to fall!
Although the action affects the person that speaks, we must use the verb "a fi" at the impersonal form here. It is an exception of the rule, because usually verbs like: a fi, a sta, a plăcea, a durea are personal. Let's take another example for "a sta": Stă să plouă = it is about to rain.
Think of it as a construction to the effect of: "It was nearly such that". "that" corresponds to "să" and the impersonal "Era" is just a description of a situation that nearly happened. The "nearly" should actually be part of the subordinate clause: "It was such that... nearly...".
It is different from English, where you can have personal form (I was about to do something) or impersonal (it was about to rain). In Romanian we always use the impersonal form, because we mean "the action" is/was about to happen = third person (era să plouă; era să cad ; era să cădem ; era să cădeți)