Tension Headache with Irritable Bowel Syndrome (IBS): This is the most likely diagnosis because tension headaches are common and can be triggered by stress, which also exacerbates IBS, leading to a rumbly stomach. The combination of these two conditions can frequently co-occur due to shared triggers.

Migraine with Gastrointestinal Symptoms: Migraines can cause headaches and are often accompanied by gastrointestinal symptoms such as nausea, vomiting, and abdominal discomfort, which could be perceived as a rumbly stomach.
Food Intolerance or Sensitivity: Conditions like lactose intolerance or gluten sensitivity can lead to both headaches (possibly due to inflammation or allergic reactions) and gastrointestinal symptoms (like bloating, gas, and stomach rumbling).
Anxiety or Stress-Related Disorders: Anxiety and stress can cause both headaches and gastrointestinal disturbances, including a rumbly stomach, due to the body's stress response affecting the digestive system.

Subarachnoid Hemorrhage: Although rare, a sudden, severe headache (often described as "the worst headache" ever experienced) could be accompanied by vomiting, which might be mistaken for a rumbly stomach. This is a medical emergency.
Meningitis: Inflammation of the protective membranes covering the brain and spinal cord can cause severe headache, fever, and sometimes gastrointestinal symptoms like nausea and vomiting.
Appendicitis: While the primary symptom is abdominal pain, some patients might experience nausea, vomiting, and headache. The pain typically starts near the navel and then moves to the lower right abdomen.

Porphyrias: A group of disorders that can lead to abdominal pain, neurological symptoms (including headaches), and psychological disturbances. They are rare and often difficult to diagnose.
Celiac Disease: An autoimmune disorder where the ingestion of gluten leads to damage in the small intestine, causing abdominal symptoms and potentially headaches due to malabsorption of nutrients.
Mitochondrial Disorders: These are a group of conditions that affect the mitochondria (the energy-producing structures within cells), leading to a wide range of symptoms including headaches and gastrointestinal issues, due to impaired energy production.