Final answer:
Severe pain in a dying loved one is the symptom that would most likely cause distress to a family member.
Step-by-step explanation:
The symptom that would most likely cause distress to a family member of a dying loved one is severe pain. This is because severe pain can be emotionally and physically distressing for both the patient and their family members. It can be difficult to witness a loved one in pain and feel helpless to alleviate their suffering. Providing adequate pain management and support for both the patient and family members is crucial in ensuring a good death as defined by the Institute of Medicine.