This chapter offers a phenomenological analysis of changes in the structure of experience that fundamentally characterise both several main forms of neuropsychiatric illness and the nature of religious commitment. The use of the portmanteau term ‘neuropsychiatric’ acknowledges the fact that many of the conditions discussed in this chapter do not fit neatly within the shifting and unclear professional boundaries of psychiatry and neurology, a problem with which other chapters in this volume engage. In this chapter, in fact, I propose that these conditions are best understood phenomenologically in a way that challenges those professional partitions. Specifically, neuropsychiatric illness and religious commitment both involve distinctive changes to the structure of first-person experience that can be characterised phenomenologically in terms of altered existential feelings – a neglected set of affective states, currently a topic of research by philosophers, psychiatrists and cognitive scientists. Later in the chapter, I go on to make the further, stronger claim that the fundamentally phenomenological character of neuropsychiatric and religious experience assigns investigative and interpretive priority to phenomenology rather than to neuroscience. As a caveat before beginning, my claim is not that neuropsychiatric illness and religious commitment are identical or that religiosity is pathological, though doubtless they can be, and indeed surely are, complexly related in many cases.1 Instead, the claim is that what a person experiences during neuropsychiatric illness and in religious commitment ought to be understood phenomenologically in terms of alterations in their existential feeling.