Problem: Paroxysmal sympathetic hyperactivity (PSH) is a complicated phenomenon that presents as autonomic instability and muscle overactivity in individuals who experience severe brain injury. Identifying potential modifiable environmental nociceptive stimuli is necessary for developing interventions that impact clinical outcomes. Objective: The aim of this study was to identify physical environmental nociceptive stimuli that could hinder recovery for children who experience PSH after severe brain injury. Methodology: This study measured quantitative physical characteristics coupled with data from semistructured interviews, with parents and clinical nurses, to explore the elusive PSH phenomenon after severe brain injury in children. Results: Eight subjects were enrolled in the cohort study. Temperature showed a statistically significant association with PSH (P = .02), with lower temperatures associated with an increased chance of PSH. Blankets were also associated with PSH (P = .009), with the use of blankets associated with a greater chance of PSH. Persons, gown, position, head-of-bed elevation, incontinence of urine and stool, light level, and noise level did not point to a statistically significant association with PSH. Six nursing interviews were conducted with 2 guardian interviews. Themes that are emerging from the qualitative interviews included the priorities of strategies to target auditory, tactile, and visual stimuli. Conclusion: Paroxysmal sympathetic hyperactivity environmental strategies need to be explored further in subsequent studies. Environmental interventions could complement pharmacological strategies for the management of this elusive phenomenon with the goal of improving outcomes in children who experience severe brain injury and show PSH.