I don’t believe in it. I astral project all the time but I don’t think there’s anything supernatural or spiritual about it besides the awesomeness of it. I’ve tried to test different things and it’s never affected the real world.
I’ve never seen a cord of any kind, but what you see is a manifestation from your mind so it’s entirely subjective to the individual.
I don’t believe that you would ever stay in a different “reality” for more than your allotted sleep. That being said, sometimes you can experience more than one day while in your projection or lucid dream. The most I have ever experienced is an astral projection, then false awakening into the following day in a congruent timeline, before actually waking up..if that makes sense. I thought it was 2 days before I woke up and it was just my normal night sleep.