Literal translation
my arms fell off me because of it
Meaning
I was flabbergasted
Explanation
The expression marks astonishment so intense that it seems to drain all strength from the body: the arms, losing their grip, fall along the body as if struck by shock. This bodily image of surprise matches its French counterpart almost word for word, which makes the phrase immediately understandable. The verb toumba (to fall) carries here the figurative sense of sudden dejection, and the pronoun en refers back to the cause of the astonishment, usually stated just before in the conversation. It is used in the past tense, the form toumbèron being the simple past, a narrative register fitting for telling an anecdote or a surprising memory. The phrase belongs to familiar speech and applies equally to bad news or to a comical revelation, the point being the gap between what was expected and what actually happens.