Not related to mirrors, but I sometimes have similar experiences when waking up, except with regards to spatial recognition: I'll lie on my bed with my eyes open for 15-30 seconds and genuinely not be able to recognize where I am or how I got there.
I sometimes cannot spontaneously remember, when waking up, where I am. It is not related to the place (usually happens in my own bed), nor to events the night before (standard evening and night) neither to the sleep phase (I usually wake up on my own).
I then need to think hard about the place, the context, etc. before rationally settling up on the place. I only then open my eyes.
