Viral Gastroenteritis: This is the most common cause of acute diarrhea, and the frequency of diarrhea every 20 minutes is consistent with a viral etiology, such as norovirus or rotavirus, which can cause rapid and frequent bowel movements.

Food Poisoning: Bacterial food poisoning (e.g., from Staphylococcus aureus, Bacillus cereus, or Clostridium perfringens) can cause sudden onset of diarrhea, which may occur at frequent intervals.
Inflammatory Bowel Disease (IBD) Flare: Patients with IBD (e.g., Crohn's disease or ulcerative colitis) may experience exacerbations of their disease, leading to frequent diarrhea.
Irritable Bowel Syndrome (IBS): Although less likely to cause such frequent diarrhea, some patients with IBS may experience episodes of rapid bowel movements, especially if they have the diarrhea-predominant subtype.

Cholera: While rare in many parts of the world, cholera can cause extremely frequent and voluminous diarrhea, leading to severe dehydration and electrolyte imbalances if not promptly treated.
Clostridioides difficile (C. diff) Infection: This bacterial infection can cause severe, frequent diarrhea, especially in individuals who have recently used antibiotics or have been hospitalized.
Intestinal Obstruction: Although diarrhea is not the primary symptom, partial intestinal obstruction can cause frequent, watery stools and is a medical emergency.

VIPoma: A rare endocrine tumor that secretes vasoactive intestinal peptide (VIP), leading to severe, chronic diarrhea (often >1 liter/day).
Neuroendocrine Tumors: Certain tumors, like carcinoid syndrome, can cause diarrhea due to the secretion of various peptides and amines.
Short Bowel Syndrome: A condition where a significant portion of the small intestine is missing or not functioning, leading to malabsorption and frequent diarrhea.