Second language (L2) postgraduate students are susceptible to experience second language writing anxiety (SLWA) in dissertation writing as they tend to find the writing process arduous. SLWA relates to the recurring negative and anxious feeling when students write which could influence their cognition, behaviour, and physical condition. This reflects the interrelationship between individual’s affect and cognitive process and the negative correlation between SLWA and writing performance reported in past studies. However, more evidence is needed to establish SLWA as an independent construct that could directly affect writing performance. Therefore, this study aimed to explore how SLWA influences L2 postgraduate students’ dissertation writing to have a clearer insight into the phenomenon. This investigation utilised a multiple-case study approach involving four local postgraduate students. Data was obtained through in-depth interviews, audio journals, and personal document analysis. The thematic analysis revealed the following themes: SLWA i) influences emotional states; ii) triggers emotion regulation; and iii) initiates and sustains a debilitative or facilitative psychological loop that influences students’ progress in dissertation writing. Thus, the study posits SLWA as a construct that can directly debilitate writing performance and L2 dissertation writing as having affective costs that makes emotion regulation an important mechanism to restore student’s psychological balance. To overcome SLWA’s influences on dissertation writing, it is recommended that supervisors and language teachers discourage perception of writing inability, recognize writing improvement, identify writing competence, suggest specific solutions to resolve writing issues, and avoid manipulating anxiety to provoke writing performance.