Viral Gastroenteritis: This condition is characterized by inflammation of the stomach and intestines, often due to a viral infection. Symptoms can include nausea, vomiting, diarrhea, abdominal cramps, and sometimes arthralgia. Hypotension can occur due to dehydration from excessive fluid loss. The combination of these symptoms makes viral gastroenteritis a plausible initial diagnosis.

Food Poisoning: Similar to viral gastroenteritis, food poisoning can cause nausea, vomiting, diarrhea, and abdominal cramps. Arthralgia might be less common but can occur, especially if the poisoning leads to a systemic inflammatory response. Hypotension could result from severe dehydration.
Influenza: While primarily known for respiratory symptoms, influenza can also cause systemic symptoms such as arthralgia, nausea, and in severe cases, hypotension, especially if there's a significant systemic inflammatory response or if the patient is dehydrated.
Medication Side Effects: Certain medications can cause arthralgia, nausea, and hypotension as side effects. For example, some antibiotics, antihypertensives, and NSAIDs can lead to these symptoms.

Septic Shock: Although less likely, septic shock is a life-threatening condition that requires immediate attention. It can present with hypotension, nausea, and arthralgia, among other symptoms. The key is to identify and treat the underlying infection promptly.
Adrenal Insufficiency: This condition, where the adrenal glands do not produce adequate amounts of hormones, can lead to hypotension, nausea, and potentially arthralgia due to the lack of cortisol. It's crucial to consider this diagnosis, especially if the patient has a history of adrenal gland problems or is on long-term steroid therapy.
Toxic Shock Syndrome: A severe condition caused by bacterial toxins, it can present with sudden onset of fever, vomiting, diarrhea, abdominal pain, and hypotension. Arthralgia might not be a primary symptom but could occur. This condition is medical emergency.

Connective Tissue Diseases: Conditions like lupus or rheumatoid arthritis can cause arthralgia and, in flare-ups or severe cases, might lead to systemic symptoms including nausea and hypotension.
Hemorrhagic Fever: Certain viral hemorrhagic fevers can present with a wide range of symptoms including arthralgia, nausea, and hypotension, though these are relatively rare and typically associated with specific geographic locations or exposures.
Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodes of hypotension (less commonly), nausea, and potentially arthralgia due to catecholamine surges affecting various body systems.