Final answer:
The patient with acute gastroenteritis symptoms should immediately seek medical treatment due to the risk of severe dehydration and the need for possibly receiving intravenous fluids. Oral rehydration solutions and other home treatments are secondary to professional medical care in this situation.
Step-by-step explanation:
The recommended action for a 75-year-old patient with symptoms of gastroenteritis—such as dizziness, weakness, significant weight loss, and difficulty keeping fluids down—is to seek medical treatment immediately. Due to the risk of severe dehydration and the age of the patient, a professional medical assessment is necessary.
While oral rehydration solutions are often used to manage dehydration, frequent vomiting and inability to keep liquids down could necessitate intravenous fluids, which require medical supervision. Over-the-counter anti-diarrheal and simple electrolyte solutions might be helpful in milder cases, but given the described symptoms, professional assessment and treatment are the priority.