I’ve experienced this too Armand - maybe on average once every three or four months. One thing that I find interesting about it is that whether it is actually a real or an imagined voice, it certainly does wake me up.
That’s interesting to me because I am a very, very deep sleeper unable to be disturbed by practically nothing. In fact, my sleep is so deep and waking me is so hard that it is sometimes an “issue” with my girlfriend. Sometimes she’ll wake up because of the slightest sound and then try aggressively to wake me to ask me, “...did you hear that?” Which is of course kind of a ridiculous question to ask if you had to beat on me for ten seconds to wake me up to ask the question in the first place!