I talk in my sleep every night?

I know that's generally harmless, but last night my cousin was watching House while I was sleeping in her room at a sleepover. She tells me that I responded to the episode with a logical observation about it, cept I said it three times. I don't even remember the episode, and I know I was asleep at the time. How is this possible, and why do I keep talking in my sleep? I wasn't aware of the problem previously. Also, every morning I wake up feeling extremely anxious and nauseous from the anxiety. Note: I'm a 16 year old female. Thoughts?