Friends of John Travolta are concerned over the health of the reclusive star.

'The Taking of Pelham 123' actor has been taking midnight drives in a golf cart alone across his Jumbolair estate in Florida.

He is said to be unable to sleep because he is grief stricken at the loss of his teenage son, Jett, six months ago.

The late night drives are a regular occurrence, according to one local resident.

A neighbour said: "We often see John driving himself around at night.

It's sad to see. You rarely catch sight of him during the day. We used to see him driving around on a buggy with his son. Now it's just John by himself."

Jett died after suffering a seizure while on a family holiday in the Bahamas in January.

Since the tragedy John has admitted Jett was suffering from autism, going against the beliefs of his Scientology religion, which does not believe in the medical condition.

After Jett's death, it was claimed John and his wife Kelly Preston's refusal to accept their son's condition meant he was not taking medication.

It has been claimed Jett was treated with detoxification programs and vitamins, rather than conventional drugs.

It has also now been rumoured John is thinking of leaving his bizarre cult-like religion – started by science fiction writer L. Ron Hubbard - after 35 years, because his faith has been so "deeply shaken" by his son's death.

"There have been strong rumours coming out of Scientology that John Travolta is disappointed that the religion was not able to help his son more," said Rick Ross, a US author and lecturer on the Scientology.

If the 'Pulp Fiction' star – who is in the upper eschelons of the religion, and has invested millions of dollars of his own money into it - does leave, the church are likely to react badly, according to Rick.

He added: "'I think it would be very difficult for John Travolta at this stage to extricate himself from Scientology.

"It would be a huge move on his part because Scientology keeps files on its celebrity members containing embarrassing personal information about them.

"And Scientology has proven in the past that it has a penchant for releasing that information to embarrass people who have left and who have said things it doesn't like.

"That's why I think Travolta will want to keep his problems with the Church private."

John and his wife Kelly – also an strict follower of Scientology – also have a daughter, Ella Bleu, nine.