A US man is struggling to cope with a condition that causes him to become paralysed whenever he feels affectionate.

Matt Frerking, 39, has narcolepsy with cataplexy, a rare disease that makes it impossible for him to enjoy a normal relationship with his wife.

In most sufferers, the paralysis is triggered by an emotional stimulus, such as laughter or boredom. For Mr Frerking, that trigger is love.

Whenever he feels affection towards his wife, stepchildren, or family, he falls into a sudden sleep attack that renders him unable to move.

During the attacks he can hear and feel anything going on around him, but he cannot move his muscles to react to the situation.

The trigger is so sensitive that Mr Frerking even falls into paralysis when he witnesses two strangers in love, ABC News US reports.

"I have to limit those things very carefully," he told the network.

Mr Frerking tries to stop the attacks by avoiding physical affection or moments of sentimentality.

His wife, Trish Frerking, keeps a blog about their life together, and said she still "feels lucky" to be with him. "I love him," the 51-year-old said.

"Frankly, he loves me or he wouldn't put himself through it. And I'm thankful I'm the person who gets to be with him most of the time."

But she admits that at times she wishes she could be closer to her husband.

"It's tough," she said. "I miss touching him ... I want to be touching him ... I miss making out."

Tags Health news diseases