If it is true, then nobody could possibly have made it back from the Astral in order to warn us. It's like saying, "There have been no reported bear attacks in this forest." It's supposed to mean that bears in this forest do not attack, but what it can also logically mean is that anybody who has been attacked does not live to report it.
That said, I don't believe it is true, only because 1.) it has never happened to me, and when I would go Astral, believe me I would go as far as possible and stay out for as long as I could! 2.) my 10th grade biology class covered a unit on the brain and nervous system, and it has stuck with me what a marvel of nature it is that we have found a way to store memories in a physical body and emotional responses and other things that people try to elevate as "spirit" or "soul" of a person. It's okay if that is, for the most part, our body after all.
It is true that a person can lose their mind. Nobody knows what is going on in the experience of somebody who is catatonic or comatose, whether that is related to astral projection or no (usually no.) But in my experience, your body will have you back no matter what. If you get hungry or you need to pee, or even if lying in the same position cut off the blood supply to your elbow or something, then you will come back automatically.