Digestion troubles -- every cat experiences them at some point or another. Problems arise when a more serious issue, such as a gastrointestinal blockage, gets dismissed as just another hairball or just another upset tummy. Cats with symptoms of a blockage need to visit a veterinarian, stat.
Two basic types of blockages affect cats -- intestinal obstructions and gastric outflow obstructions. The latter tends to occur when something blocks the path between the stomach and small intestine, making it difficult or impossible for food to pass beyond the stomach. Intestinal obstruction occurs in either the small or large intestine and can be partial or complete.
The simple answer? Some object keeps food from being able to pass through Kitty's digestive tract. That object can be any number of things, foreign or organic. Does your cat play with strings or yarn? If so, he could have slurped one down. Same with small toys or buttons. Tumors or ulcers can keep food from passing through the kitty's system, as can organ swelling. Severe constipation causes stool to become impacted, which forms a block. Worms, particularly roundworms, multiply and form a mass in the intestines. Left untreated, a blockage develops.
Don't be so quick to discount vomiting as just another tummy trouble. It's one of the primary symptoms of gastric outflow obstructions. If the intestines are blocked, look for lack of appetite, constipation, weight loss and abdominal discomfort. Does your kitty strain to poo in the box? If he works hard but nothing or very little comes out, get him to a veterinarian as soon as possible.
If your cat can't go, he won't live long. It's vital that he receive swift treatment from a knowledgeable veterinarian. That treatment depends on what caused the blockage. If there's a foreign object in there, the vet may recommend surgery to remove it. If tumors or ulcers are the issue, you'll have to treat the underlying cause. Resection -- the removal of part of the stomach or intestine -- could be necessary.