Psychiatrist Stuart Grassian has proposed the term "SHU syndrome" to name the cluster of cognitive, perceptual and affective symptoms that commonly arise for inmates held in the Special Housing Units (SHU) of supermax prisons. In this paper, I analyze the harm of solitary confinement from a phenomenological perspective by drawing on Husserl's account of the essential relation between consciousness, the experience of an alter ego and the sense of a real, Objective world. While Husserl's prioritization of transcendental subjectivity over transcendental intersubjectivity underestimates the degree to which first-person consciousness is constitutively intertwined with the embodied consciousness of others, Husserl's phenomenology nevertheless provides a fruitful starting-point for a philosophical engagement with the psychiatric research on solitary confinement.