This study explored the flow experience and physiological responses during a mirror-tracing task performed in both real-world (REAL) and virtual reality (VR) environments. Seventeen healthy participants completed the task under two feedback conditions—a self-paced tracing condition (NORMAL) and a self-competitive condition (GHOST)— where participants attempted to trace faster than their own prior trajectory. Both conditions were carried out in REAL and VR environments that replicated an identical workspace. Each session included a 5-min resting phase followed by two 5-min task trials. Subjective measures (flow experience, mental workload, and simulator sickness) and physiological responses (heart rate [HR] and heart rate variability [HRV]) were collected and compared across conditions. The results indicated that, regardless of the environment, the GHOST condition significantly enhanced perceived feedback and task accomplishment scores on the Flow State Scale. Mental workload was lower in GHOST, whereas temporal demand and frustration scores were notably higher, particularly under the VR condition. Simulator sickness scores indicated a mild increase in oculomotor symptoms during VR use; however, no severe discomfort was reported. HR did not show significant differences between conditions; however, HRV indices showed notable changes. Specifically, low-frequency (LF) power and the LF/HF ratio decreased substantially during task performance in both environments, indicating parasympathetic dominance typically associated with sustained attention. In the VR condition, a transient reduction in LF/HF during the first task block may reflect initial sensory adaptation to the immersive environment. These findings suggest that while self-competitive feedback can facilitate components of the flow state, immersive VR environments introduce sensory and cognitive demands that may disrupt the sustained flow. Additionally, HRV indices such as LF and LF/HF emerged as sensitive indices of attentional engagement. Although HR was less responsive to task variations, it demonstrated temporal stability and may serve as a complementary indicator for real-time monitoring in VR-supported task environments.