The present study explored the phenomenological characteristics of anomalous experiences (AEs) reported during Umbanda rituals, a mediumistic Brazilian religion, with the aim of comparing AEs reported during rituals involving the use of Ayahuasca (an entheogen frequently used in some Umbanda contexts) and rituals without the use of this substance. In order to do so, we compared individuals with different levels of involvement with the mediumistic practices. The study was based on an auto-ethnographic approach. This methodological perspective allowed us to confront subjective data with the available knowledge in the scientific literature about AEs, dissociative phenomena and altered states of consciousness and was of fundamental importance for a more sensitive understanding of the nuances and characteristics of these experiences. The results attest to a significant similarity between the experiences reported with and without the use of Ayahuasca in mediumistic contexts. In both groups, the experiencers were able to identify certain similarities in their experiences regarding a reduction of voluntary motor control, changes in memory and perception, communicability and accessibility of experiences, anomalous information reception and increases in interpersonal sensitivity. The results support the methodological feasibility of autoethnography as a research tool and point to its relevance to a deeper understanding of AEs and other subjective experiences usually of difficult investigation by other research methods.