Strange intruder in an imagined scene

[Nembra]

Few years ago I was doing something akin to Jung's active imagination technique - details are of secondary importance, basically controlled daydreaming. I was talking to some lesser spirits that manifested in a memory of a pleasant glade I used to visit in my childhood. The conversation was authentic if not very memorable, but the whole scene wasn't very independent and required quite some conscious awareness to keep stable. That is, until at some point I felt a very alien presence, followed quickly by an intrusion of... something. It was a colossal mass of facets, like pieces of shattered glass or insanely complex origami, but as if made of slightly opalescent air - it was difficult to get a good look at it. It rolled as if its structure contained some impossible, crystalline wheels. Despite feeling - and sounding - incredibly heavy the trees it went through remained untouched. I felt compeled to lie down motionless to avoid disturbing its passage. As it appeared from north (roughly) so it departed towards the south., it didn't interact with me (or anything else) in any way. I didn't see anything like that before or after. It showed up completely unprompted as if its path just happened to go through my mind's eye while I was fully awake.

Have you ever heard of or experienced anything like that? Nothing that would answer my questions has anything useful to say.