One of the more unexpected occurrences when receiving Reiki, can be what I am going to collectively call "Reiki Visions".
These take the form of audio, visual, physical sensations, or informational downloads for the receiver of the Reiki Fire. They take place during the session, and regardless of the form they take, the experience is remarkable and serves to provide neccessary information and assistance. It is actually a really wonderful experience!
During my sessions as a client with my own Reiki Practitioner (because of course I invest in Reiki services myself too), I have personally experienced hearing sounds and voices, had sudden knowledge about what had previously been hidden, and always loads of imagery! Now not everyone will have these kids of clairvoyant experiences, but I think it is quite common and more
I have found the visions to be helpful in so many ways. It is not something to be feared, but to be embraced. Know that your higher self and spirit guides will not allow you to experience a vision during a Reiki Session that is not in the best interest of your higher self.