In Old Irish the word aislinge means both dream and vision, and it used to be that the two concepts in most cultures - pagan and Christian - were not sharply divided as we might find them viewed today. A dream and a vision were two possible terms for the same experience, and both were things that occured when the spirit went somewhere or communicated with something while the body slept. In records we have of visionary experiences often the person relates being taken somewhere and directly seeing or participating in events which may be portentous or divine (in the case of Christian visions) or may involve the person being taken to Otherworlds (in the case of pagan dreams and later the dreams of the common people). The common thread that unites these narratives is the idea that what was seen and experienced was real and valid on its own merits and that this reality was tangible i.e. could have physical effects in the waking world. People might correctly predict an event based on what was seen in a dream-vision or they might wake with a physical token of their nighttime experiences, be that marks on their body or an actual item brought back from their wanderings*.
It was not uncommon for a person, while dreaming, to travel to Fairy or to be contacted by Otherworldly spirits, or even for a person's spirit to travel out in this world. There was an implicit belief that what occured to and with us while we slept was just as real as what occured while we were awake. We find stories in mythology like the Aislinge Oenguso of a woman who appears to the deity Oengus at night while he dreams but has a noticeable physical effect on him and who has an unquestionable reality. In folklore there are stories of people who might spend years in the Otherworld while only moments passed here and they appeared to onlookers to be sleeping or in a trance. In one such story a man who seemed to sleep for a few minutes in a field experienced several years living in Fairy, enjoying a pleasant time there until he broke a taboo and was banished, finding himself sent back to the time and place he left. We also have stories of medieval witches who would be seen sleeping in their beds while they were simultaneously seen by other people elsewhere awake and active. It seemed that the soul was as busy at night as it had been during the day, the only difference being whether it made use of the body or not.
The erosion of the value of dreaming would eventually begin with Christianity's attempt to control the powerful messages gained through dreams. This was done by creating a hierarchy wherein ecclesiastical dreams and visions were direct connections to God but the dreams and visions of the common people were delusions relegated to vulgar spirits, demons, and witches. Dreaming became a dangerous thing during the witchcraft persecutions; dreams were seen as a time when we could be opened up to unsavory influences and attacks, and when we ourselves might be out harming others and unable to offer any defense if accused of doing so. We see dreaming as a double edged sword, a weapon of the Church for control and an unsafe activity of those outside Church bounds. Dreaming slowly lost its sacredness entirely on the altar of rational thought and became nothing more than another aspect of the mind to be dissected. This desacralization of dreaming began the descent of the dream from something profound to something almost meaningless and difficult to interpret, an individual language that only the dreamer spoke, a puzzle to be solved.
If we look at dreams and dreaming we might perhaps find that it is not dreams that have changed but only our own understanding of them. Our culture has trained us now to see dreams as trivial things, as the mind talking to itself and as the body's response to imbalance. Dreams can be a way for our mind to talk to itself and work out problems, of course, however dreams are complex and diverse and sometimes they are a way for our soul to connect or move outwards. Certainly not all dreams are journeys Elsewhere, but sleep is still the liminal gateway for our soul to travel out that it has always been. Dreams are still an opening for different spirits to communicate with us, a time when our minds are still and receptive in ways they often are not while we are awake. This idea of communication with spirits during dreams is very old and something we see in folklore with everything from ancestors to landspirits to the Good People to Gods.
I have always personally believed in the reality of dreaming, and I think there is value in other people evaluating this concept more generally which is why I chose to write about it. Dreams are more than just stories our minds tell ourselves while we sleep, at least sometimes. Sometimes what we dream is as real as what we do in our waking life, and that matters because it means that we need to take dreaming a lot more seriously. It can be a gateway to Fairy, and other worlds besides, and what we do there can impact is here. We need to remember to protect ourselves, and that the same rules apply for safe travel in dreams as in meditations or spirit journeys. Because if dreams are real then we can be hurt in them, we can swear oaths in them, we can make mistakes in them that follow us back here; and we can earn blessings as well (its not all bad after all).
Lecouteux, C., (2003) Witches, Werewolves, and Fairies: shapeshifters and astral doubles in the middle ages
Bitel, L., (1991) "In Visu Noctis": Dreams in European Hagiography and Histories
Briggs, K., (1976) Dictionary of Fairies
Evans-Wentz (1911) Fairy Faith in Celtic Countries
Firth Green, R., (2016) Elf Queens and Holy Friars
Aislinge Oenguso http://iso.ucc.ie/Aislinge-oenguso/Aislinge-oenguso-text.html
*I'm not going to address here the various scientific attempts to explain these phenomena.