Yes, I know it's daydreaming because our real senses are still connected, so any touch or movement will snap us out of it in a way that can't happen with normal sleep.
It is actually how we discovered that our daydreams are non-lucid: we were trapped in one for around three hours, and completely forgot the body even existed, until it felt a movement and we suddenly snapped out of the daydream.
This has been true for our entire life, though. Being in a dream or daydream has always unconditionally caused us to be certain that it is reality. It is not possible for us to doubt what we perceive, even if it really is our imagination, no matter how random or unbelievable it is.
We just sort of know what we saw, and therefore, it happened the way we saw it even if it isn't obeying the laws of physics or science.
(We have many examples of full dreams where any reasonable person would have become lucid, but we did not because we were already fully certain that we were not in a dream. And then we eventually woke up, go figure.)
You may notice this is very adjacent to psychosis...