Why does lucie faint upon hearing Mr Lorry's story in A Tale of Two Cities?

After she faints a woman runs into the room (A+LS)

Lucie had lived many years without her father and believed him dead. Lorry tells her, rather bluntly, that is her father alive and has been released from prison. The surprise and emotion of the moment cause her to faint. (The incredibly tortuous corsets women wore at the time, squeezing her internal organs, had nothing to do with it, I'm sure.)