I’ve never experienced something like what you’ve explained but it does sound intriguing. It reminds me of automatic writing, a method of divination or spirit communication that involves writing. Is there any way you can maybe record yourself while you sleep and see what you’re writing? Or maybe you can even attempt an automatic writing session in a trance or while in a meditative state.
Here are some resources I found for automatic writing! Some of these links go outside the forum.
→ Automatic writing attempt #2 [forum]
→ 🕚 Weekly Witchy CHALLENGE - Catch-Up! - #9 by mary25 [forum]
→ Automatic writing - Wikipedia
→ automatic writing | spiritualism | Britannica
→ Automatic Writing: How to Channel Your Soul's Wisdom ⋆ LonerWolf