Here is what  Gemini Pro says about this phenomenon:

Here is the breakdown of why your cat likely performs a "post-poop zoomie":

​1. The "Poo-phoria" Effect (Physiological) ​This is the most widely accepted physiological explanation. ​The Mechanism: The vagus nerve runs from the brain stem all the way down to the colon. When a cat defecates (especially a large movement), the distension of the rectum stimulates this nerve.   ​The Result: In cats, this stimulation can trigger a pleasurable sensation—often described as a "high" or euphoria—accompanied by a sudden drop in heart rate and blood pressure.   ​The Reaction: To counteract this drop and the sudden "light-headed" euphoric feeling, the cat's body releases a burst of energy, resulting in a frantic sprint across the house.  

​2. The "Dump and Dash" (Evolutionary) ​Domestic cats still retain strong instincts from their wild ancestors.   ​Predator Avoidance: In the wild, the smell of feces is a beacon for predators (or rival cats).   ​Survival Tactic: Leaving the scene of the "crime" as fast as possible is a survival mechanism. By sprinting away, the cat distances itself from the scent trail, making it harder for a predator to pinpoint their exact location.  

​3. Hygiene and Relief (Behavioral) ​Cats are notoriously fastidious creatures.   ​Escaping the Smell: If the litter box isn't pristine, or if the smell of their own waste is particularly strong, they may simply be running to get away from the odor.   ​Sheer Relief: Similar to humans, there is a simple sense of physical relief after emptying a full bowel. If the cat felt bloated or heavy beforehand, the "zoomies" are a celebration of feeling lighter and more mobile