February 5, 2017; revised April 25, 2020; February 26, 2023

The evidence comes in three general types of accounts, as discussed below.

1. Many people have at least briefly experienced an “out-of-body experience” (OBE), where the mental body comes out of the physical body, and one sees one’s physical body from above.

In his book, “Travels,” the famous author of Jurassic Park, Michael Crichton (1988, p. 307), mentions his ability to “shift my awareness out of my body and move it around the bedroom.” He says, “..I didn’t think anything about it… I assumed that anybody could do it..”.
A similar account has been given by a woman recently who also thought that “everybody could do it”: https://abcnews.go.com/Health/woman-body-experiences/story?id=22825927
Robert Monroe (see #6 below) says the mental bodies of most of us come out and wander around even without us realizing it. Sometimes, we are in a dream state (we believe), then feel a “sudden fall” and wake up. He says this “dream state” is the mental body wandering around, and we feel the “sudden fall” when the mental body re-enters the physical body.
So it is incorrect to assume that a gandhabba or the mental body is a “ghost.” In a sense, it is a better representation of us than our physical bodies that are discarded after about 100 years because they may live for thousands of years until the kammic energy for this human bhava is exhausted.

2. There are other — more dramatic — reported cases of OBE, some of which involve “near-death experiences” (NDE), where the person was presumed dead but revived later on. During that time, the mental body usually “went through a tunnel” to another dimension but returned to re-enter the body. See “Near-Death Experiences (NDE): Brain Is Not the Mind.”

Of course, there are many books written on OBE and NDE. “Consciousness Beyond Life” by Pim van Lommel (2010) gives detailed accounts of case studies of OBE and NDE experienced by people undergoing heart operations, some of whom were declared dead but returned to life.
A third category involves the rebirth accounts of children who were killed in an accident in their previous life. They can recall that incident from their previous life, where the mental body came out of a physical body, and they watched the accident scene from above. They have provided accurate accounts of that scene. I will discuss one such account at the end of the post.

3. The experiences described in the accounts below need to be evaluated with the following nuances (subtle aspects) in mind. Once the mental body comes out, it can be an exhilarating experience to be free of the heavy physical body. So, most people describe it as a “liberating experience.”

However, without the physical body, one cannot enjoy smells (in many cases), food tastes, and bodily pleasures. Thus, if one lived without a physical body for a long-time, one could become frustrated and suffer. This is the status of a gandhabba in between two consecutive human births.
Therefore, even though it could be a “liberating experience” to come out from the shackles of the physical body for a short time, as in OBE and NDE, it may not be that pleasant to stay in that state if one has not given up the desire for sensual pleasures since one cannot “enjoy” sensory pleasures without a physical body.

4. The other point to remember is that many experiences (especially those from the Western world) are from people with other religious backgrounds. In a way, this is good because we can get an unbiased opinion. But, unfortunately, they have a different bias due to their own religious beliefs. For example, many say they visited heaven, which could be a “good locality” of the gandhabbā.

Remember that the gandhabba world is not just “one place,” even though physical locations cannot be assigned. It is much better to say that “good gandhabbā” with higher moral values hang out together (such localities may be referred to as “heaven”), and “bad gandhabbā” segregate away from those. And there can be wide varieties in between.
It is similar to the case of people with similar gati hanging together.
So, it can be thought of as many “gandhabbā worlds” in the nether world or para lōka.
Some of the gandhabbā have very fine bodies, but others may have more dense bodies (still much less dense than ours). Some may “look” like humans, but some may have already started transforming into animal forms (due to the types of saṅkhāra they cultivate) and may look half human and half animal. It is a very complex world.

5. Robert Monroe has written several books about the OBE experiences of himself and others. Two of his books are: “Journeys Out of the Body: The Classic Work on Out-of-Body Experience” and “Far Journeys.”

Here is how he describes his first OBE experience (there are many other youtube videos on his accounts):

6. Here is an interesting documentary, “Beyond Our Sight – documentary”. Thanks to Mr. Johnny Lim from Singapore for sending me this video.

7. In their book, “Soul Survivor: The Reincarnation of a World War II Fighter Pilot”, by Bruce and Andrea Leininger detail the amazing story of their son’s recount of a past life, mentioned in the above video. There the little boy vividly describes how he died in his previous life. This falls into the third category that I mentioned in #1 above. Here is an ABC News report on the story:

8. Some scientists believe that these are mind-made hallucinations. Here is a researcher’s account of his investigations into that possibility. He started the project to prove it was a hallucination but convinced himself otherwise.

9. some people are trying to make money, saying they can teach how to do “astral projection.” Astral projection is another name for OBE.

This is not something that can be taught. So, don’t waste money.
The only way to do it systematically is to cultivate Ariya or anariya jhānā to the fourth jhāna. Then one can practice further and learn how to remove the mental body from the physical. The Buddha compared this to removing a sword from its sheath.
However, most people who can naturally do it get it as a sansaric habit. They are likely to have cultivated jhānā and developed abhiññā powers in recent past lives.
The most common situation is when the mental body pops out of the physical body in highly stressful situations where the stress affects the heart. The hadaya vatthu of the gandhabba overlaps the physical heart, and thus when the heart is stressed out, gandhabba may pop out of the body.

10. The idea of a mental body controlling the physical body is discussed in the previous post in this section (“Our Mental Body – Gandhabba.”)

By the way, the mental body is not all mental. It has a fine material component at the suddhāṭṭhaka level; see “Gandhabba (Manomaya Kaya)- Introduction” and “The Origin of Matter – Suddhāṭṭhaka.”

Many reported instances of this mental body come out of the physical body, and I have mentioned some of those in other posts. But I would like to have some of that evidence in one place to understand why it is not an alien concept.
But there are many made-up stories too. So, I advise you not to get carried away too much about watching these youtube videos. That is a waste of time. I just wanted to explain that the mental body (gandhabba) is natural.
More information at, “Mental Body – Gandhabba,” “Gandhabba (Manomaya Kaya),” and “The Grand Unified Theory of Dhamma.”