Final answer:
The patient's experiences of stomach pain, a feeling of heat, and heartburn are subjective data as they are based on the patient's personal experiences and cannot be measured objectively without medical evaluation.
Step-by-step explanation:
In the provided scenario, the data described as the patient experiencing an occasional increase in stomach pain, a "feeling of heat" in her abdomen and chest at night when she lies down, and increased incidents of heartburn can be labeled as subjective. This is because these are personal experiences reported by the patient that cannot be objectively measured or clinically confirmed without further medical evaluation. In contrast, objective data would include measurable factors such as vital signs or laboratory test results that provide concrete evidence of a patient's health status.