As per Eastern occult, we have seven bodies: the physical, the etheric, the astral, the mental, the spiritual, the cosmic, and the nirvanic. Each body has its own type of dream. The physical body is known in Western psychology as the conscious, the etheric body as the unconscious, and the astral body as the collective unconscious.
Dream Yoga is also known as lucid dreaming or astral projection, the etheric body can travel in dreams. There is every possibility of it leaving your body. When you remember it, it is remembered as a dream, but it is not a dream in the same sense as the dreams of the physical body. The etheric body can go out of you when you are asleep. Your physical body will be there, but your etheric body can go out and travel in space. There is no space limiting it; there is no question of distance for it. Those who do not understand this, who do not recognize the existence of the etheric body, may interpret this as the realm of the unconscious.
So when spiritual practitioner goes deep in meditation and sees colors, and experiences perfumes and sounds and music absolutely unknown, these too are dreams, dreams of the etheric body. So-called spiritual visions belong to the etheric body; they are etheric dreams. Gurus revealing themselves before their disciples is nothing but etheric travel, etheric dreaming.
Ancient eastern mystics have been using astral dreaming to go into previous births. That is third dimension of dreaming. But because we have only searched the mind at one level of existence, the physiological, these dreams have either been interpreted in the language of the physiological or discarded, neglected.
Sometimes in an ordinary dream, part of the etheric or part of the astral may be there. Then the dream becomes a muddle, a mess; you cannot understand it. Because your seven bodies are in existence simultaneously.