Jett Travolta's autopsy revealed that he died from seizure disorder.

That rules out, for all intents and purposes, the fact that Kawasaki Syndrome, from which Jett suffered at Age two, had any bearing on his death. The only known long-term effect of the disorder is weakening of the walls of the arteries, which can cause an aneurysm. It does not rule out autism--a condition which his parents have long denied that Jett had. Children with autism are more prone to seizures.

The Church of Scientology, to which both of Jett's parents, John Travolta and Kelly Preston, belong does not recognize autism as a legitimate health condition.

Jett, who his parents acknowledged had a "developmental disorder" that they blamed on the Kawasaki Syndrome, had a history of seizures.

A seizure is a sudden disruption of the brain's normal electrical activity accompanied by altered consciousness and/or other neurological and behavioral manifestations. Epilepsy is a condition characterized by recurrent seizures that may include repetitive muscle jerking called convulsions. Its cause is unknown.

According to a Travolta family attorney, he had previously been on medication but had ceased taking it when it stopped working and his parents became concerned about its side effects.

Recently, according to sources close to the family, he had been experiencing about a seizure a week.

Though there are many kinds of seizures, the type Jett Travolta had Friday morning was most likely a grand mal seizure.

A generalized tonic-clonic (grand-mal) seizure begins with a loud cry before the person having the seizure loses consciousness and falls to the ground. The muscles become rigid for about 30 seconds during the tonic phase of the seizure and alternately contract and relax during the clonic phase, which lasts 30-60 seconds. The skin sometimes acquires a bluish tint and the person may bite his tongue, lose bowel or bladder control, or have trouble breathing.

A grand mal seizure usually lasts between two and five minutes, and the person may be confused or have trouble talking when he regains consciousness (post-ictal state). He may complain of head or muscle aches, or weakness in his arms or legs before falling into a deep sleep.

If seizures are not completely controlled, people are twice as likely to die as those who do not have seizures. A few people die suddenly for no apparent reason—a complication called sudden unexplained death in epilepsy.

Some information provided by: https://www.merck.com/mmhe/sec06/ch085/ch085a.HTML