This paper considers how mental states can be conveyed by metaphorical expressions in texts of a personal nature. Figurative language is understood to play an important role in the expression of such complex nuanced phenomena (Lakoff & Johnson, 1999; Kovecses, 2000; Gibbs, Leggit & Turner, 2002). This study focuses on two main groups of metaphors, linked to mental states, in the Smith Journal of "The Unabridged Journals of Sylvia Plath". 'Mental state' here refers to various aspects of cognitive functioning, but with a focus on mental states of affect mental states that are intrinsically valenced (Ortony & Turner, 1990). Specifically, this paper focuses on metaphors of MOTION and SPLIT SELF. Both manual intensive analyses and automated corpus methodologies are employed in the investigation: Wmatrix (Rayson, 2009) is used to explore relevant expressions, in order to obtain a comprehensive understanding of metaphor groups. Relevant expressions are identified by an in-depth manual analysis of sample journal entries. The MIP procedure (Pragglejaz, 2007) is used for metaphor identification, and interpretations draw on research in psychology. Metaphors of mental states are analyzed in terms of their implications for conveying various aspects of mental states, such as valence and intensity.