Talking in your sleep is not unheard of.... I don't know that much about it, but I think it is akin to sleep walking in a way...
It very well could be induced by increased stress.... Maybe you have been extra busy, you are anticipating something in the future... Who knows... OR
it could be that part of your brain not fully shutting off ( Or what ever you want to call it)
You know when you fall asleep, you Your brain shuts down certain parts which normally keep you from getting up and acting out your dreams or speaking
them out, or what have you... But some times it does not work right, and you may get up and walk, or talk....
My sister used to talk in her sleep all the time when she was little, and I used to sleep walk all the time... We both stopped as we got older...
If it worries you I would suggest making an appointment with a doctor to discuss it, and see if there is anything that can be done about it.... If
anything does in fact need to be done...