Have you ever had a sleep study done before? Sometimes, sleep apnea has been linked to nightmares and sudden-wakefulness. Or, you could have that sleep hallucination that happens when you're between sleep stages. That's what it sounds like to me but I'm not a sleep doctor. I've had those types of auditory sleep hallucinations. My sleep doctor confirmed this happens between sleep stages, when our conscious mind and subconscious mind cross paths when they aren't supposed to, in simple non-scientific terms. Sometimes, I'll wake up hearing someone from my dream talking to me, or I'll wake up in the middle of a conversation and I'm talking. It's either a sleep hallucination for me, or my mild sleep apnea gets triggered when I stop breathing temporarily and my body wakes me up.