I do some self-healing practice (taught to me by the spirits I work with). A major component is going into a trance wherein I switch from being in the familiar here and now, to some other form of perception - often where I will experience my body as a transparent, hollow system of energetic tubes and valves, and or where I will be partially outside of my body looking at my body. The experience is often like lucid dreaming, but instead of trying to wake up in a dream state, I'm sinking into an intermediate state deliberately and trying to hold it. I've been getting better at this. When I do healing work from within this particular altered state of consciousness, I will see/feel/smell/touch the things I'm working with just like I'm doing by typing at you right now - it's like switching between modes of perception, frames of reference - there's something about it that's very hard to describe but I imagine it's like switching your radio from AM to FM. (As an aside which will become relevant shortly, for whatever reason, when I run into other people while doing this method, I often experience them as some kind of family relationship - brother, sister, mother, etc. - having nothing to do with being related in this reality. No idea what this signifies yet.)
I've seen some "weird" things (parasitic entities, foreign objects being the most common) but until this one experience, nothing weirder.
The last time I did it - I experienced myself as being attached, via some kind of an umbilical cord (that looked and felt real), to another entity (who looked like a human girl or young woman), who (during the experience) I thought was my sister - I'm an only child. The cord seemed to go straight through my navel to my spine, with numerous filaments wrapped around my spine. I couldn't dislodge it. It seemed to be gripping the other person the same way.
I ended up doing nothing, I couldn't think of a way to dislodge that cord without doing damage to myself.