Speaking out loud made me wake up.

[Jarrod]

I was lucid dreaming and started asking to see my guide.  I've never met him/her/it/them whatever and was curious.  I was inquiring mentally and after a few tries and nothing happened I decided to speak the request out loud.  As soon as I tried to talk either the sensation of my mouth moving or hearing the sound out loud or both brought me back to my body.  Does talking out loud have this effect with anybody else?

[Xanth]

It brought your focus squarely back to the physical.  So yeah, you wanna try to avoid it... but sometimes it's unavoidable.

[Jarrod]

I had kind of the same effect once when I was little having a nightmare.  I realized that I was dreaming, only time I remember that happening when I was little, and shut my eyes as tight as I could and when I opened them my physical eyes opened and I woke up.  I read a lot about people talking in their OOBEs though and they usually don't say it was just mental.