Okay.
There seems to be two distinct ways of looking at the ufo phenomena.
The 'nuts and bolts' type, made in a similar way to how we make things, and is a solid artifact much as our spacecraft are.
Then there is the 'They are not actually 'there' , but are an artifact of out mind. I think Jung tends to this.
But what is meant by 'not actually there ?
Saying it is all in the mind is simplistic and, frankly, somewhat disparaging.
Unless the mind is acting as some kind of portal to some other realm. A realm occupied by the things we see on occasion.
Some years ago the following happened to me.
I was sitting in my dining room, which overlooks the local pathway going from the area to the main road. This path is frequently used., being the shortest way to the bus stop.
My wife was at work. and I was home as I was only working mornings.
I glanced up and saw her walking down the path. It was about the time I would expect to see her coming from work if she had finished at 4 pm.
I didn't give it any more thought and expected her to come into the house in about 30 seconds. But she didn't.
About five minutes later, a neighbor called looking for her. I said she wasn't here, but that I suspected she may have stopped off to talk to someone as I had sen her walk down the path.
I then went back to my book.
Just after five I again saw her walking down the path. This time with our daughter.
When they came in I mentioned that I had seen her an hour ago.
She responded that I couldn't have as she was then still at work. She had me our daughter on the bus home. 5pm out of town.
So what did I see ?
It was definitely her the first time. Same build, hair, clothes, shopping bag, way of walking. Absolutely no doubt. And I had ample time to look.
The only difference between the two sightings was that on one occasion the cardigan she was wearing was buttoned up, and on the other it wasn't.
It was some kind of apparition. A totally lifelike viewing of something that wasn't there. So real that I didn't give it a second thought.
This brings us to the second class of ufo sighting. The class where not everyone in an area see what some report. Is there some kind of circumstance where they are looking at something that is somewhere else. Not actually there. ?
As for the difference between apparitions and hallucinations.
I suspect that hallucinations are generally brought on by stress or some other mental problem. They also have a feeling of 'unreality' about them.
An apparition is very lifelike.
And like the people who claim to see ufos. i can only say that know what I saw. But there is no way of proving this.