I have had a few cases where a voice has intruded when I was tired, but not about to fall asleep (in one case I was driving). In each case the voice was not tal

I have had a few cases where a voice has intruded when I was tired, but not about to fall asleep (in one case I was driving). In each case the voice was not talking to me at all, and it was just a snippet, less than a sentence, and then it's gone and does not recur. It is almost as if I am eavesdropping on a bit of random conversation. I have never experienced a visual hallucination (and I have never taken any drugs that could cause either).