Gallstones or Cholecystitis: The symptom of feeling something stuck in the right upper quadrant that improves with lying down is suggestive of a gallbladder issue, such as gallstones or cholecystitis. Position changes can exacerbate gallbladder pain due to movement of gallstones or increased pressure on an inflamed gallbladder.

Gastroesophageal Reflux Disease (GERD): Although more commonly associated with heartburn, GERD can cause a sensation of something being stuck, particularly if acid reflux irritates the upper gastrointestinal tract. Symptoms can worsen with position changes and may improve when lying down.
Peptic Ulcer Disease: A peptic ulcer in the duodenum or stomach can cause pain that is exacerbated by position changes and may feel like something is stuck. Lying down can sometimes alleviate the pain by reducing acid production or changing the position of the ulcer relative to the stomach contents.
Hepatic or Renal Pathology: Conditions affecting the liver or right kidney, such as hepatitis, liver abscess, or pyelonephritis, can cause right upper quadrant pain that may worsen with movement or position changes.

Pulmonary Embolism: Although less likely, a pulmonary embolism can cause sudden onset of chest pain that may radiate to the right upper quadrant and can worsen with deep breathing or position changes. It's crucial to consider this diagnosis due to its high mortality rate if untreated.
Myocardial Infarction: Cardiac issues, including myocardial infarction, can sometimes present with atypical pain that may be felt in the right upper quadrant, especially if there is referred pain. The improvement with lying down does not rule out cardiac causes.
Hepatic or Splenic Rupture: Traumatic injuries to the liver or spleen can cause severe pain that may be exacerbated by movement. Although these conditions are emergencies and would likely present with more dramatic symptoms, they should not be overlooked.

Diaphragmatic Hernia: A diaphragmatic hernia can cause abdominal contents to herniate into the thoracic cavity, leading to pain that may be exacerbated by position changes and could feel like something is stuck.
Intra-abdominal Shunt or Adhesions: Rarely, intra-abdominal shunts or adhesions from previous surgeries can cause intermittent obstruction or kinking of bowel loops, leading to pain that may be position-dependent.
Tumors of the Liver, Gallbladder, or Bile Ducts: Although less common, tumors in these areas can cause obstructive symptoms or pain that may worsen with position changes due to the mechanical effects of the tumor.