How does it feel to lack a sense of boundaries? A case study of a long-term mindfulness meditator

•Sense of boundaries (SB) should be defined in terms of flexibility.•The more flexible the SB, the weaker the sense of self becomes.•The more flexible the SB, the weaker the sense of ownership and agency become.•In the absence of SB, one nevertheless experiences general bodily feelings.

This paper discusses the phenomenological nature of the sense of boundaries (SB), based on the case of S, who has practiced mindfulness in the Satipathana and Theravada Vipassana traditions for about 40 years and accumulated around 20,000 h of meditative practice. S’s unique abilities enable him to describe his inner lived experience with great precision and clarity. S was asked to shift between three different stages: (a) the default state, (b) the dissolving of the SB, and (c) the disappearance of the SB. Based on his descriptions, we identified seven categories (with some overlap) that alter during the shifts between these stages, including the senses of: (1) internal versus external, (2) time, (3) location, (4) self, (5) agency (control), (6) ownership, and (7) center (first-person-egocentric-bodily perspective). Two other categories, the touching/touched structure and one’s bodily feelings, do not fade away completely even when the sense-of-boundaries disappears.