Perforated Peptic Ulcer: This condition is characterized by severe abdominal pain that worsens with movement and deep breathing, as well as lying down, due to the irritation of the peritoneum by gastric acid.

Gastroesophageal Reflux Disease (GERD): Symptoms can include abdominal pain that worsens with lying down and may be exacerbated by deep breathing due to increased pressure on the lower esophageal sphincter.
Pancreatitis: Abdominal pain associated with pancreatitis can radiate to the back and worsen with lying down and deep breathing due to the retroperitoneal location of the pancreas.
Cholecystitis: Inflammation of the gallbladder can cause right upper quadrant abdominal pain that may worsen with deep breathing and movement, including lying down.

Pneumoperitoneum: Free air in the abdominal cavity can cause severe abdominal pain that worsens with movement and deep breathing. Although less common, missing this diagnosis can be catastrophic.
Myocardial Infarction: Although primarily presenting with chest pain, myocardial infarction can sometimes manifest as abdominal pain, especially if the inferior wall of the heart is involved. The pain can worsen with exertion, including deep breathing.
Pulmonary Embolism: While primarily a respiratory issue, a large pulmonary embolism can cause referred abdominal pain due to the involvement of the diaphragm, which can worsen with deep breathing.

Diaphragmatic Hernia: A rare condition where abdominal contents herniate through the diaphragm, potentially causing abdominal pain that worsens with deep breathing and lying down due to increased pressure on the herniated contents.
Splenosis: Ectopic splenic tissue can cause chronic abdominal pain, which might worsen with certain positions or deep breathing, although this is a rare and less likely cause.
Abdominal Migraine: A condition more commonly seen in children, characterized by recurrent episodes of severe abdominal pain, which can be exacerbated by various factors including position and breathing.