The former lover of a woman left paralysed after she was "catapulted" from her bed during sex said at first he laughed at her fall, before realising she was seriously hurt.
John Marshall said he saw Claire Busby roll backwards off the bed "in slow motion", as she shifted her position.
The 55-year-old, from Alloa, Scotland, said it was "the worst thing that had ever happened" in his life.
Ms Busby is suing the suppliers of the bed, who contest the case.
Ms Busby, from Maidenhead, Berkshire, suffered a serious injury to her spine in August 2013.
Mr Marshall said the incident had affected him "very badly".
He said in a witness statement to the High Court that, after the fall: "I was expecting her to get up, and when she didn't I laughed and said, 'get up', but she said that she had hurt herself.
"She said she could not feel her arms and legs. I thought she was joking and I laughed."
Mr Marshall added: "She told me again that she had hurt herself and to call an ambulance."
The businesswoman claims the bed was in a "defective state" at the time of her accident and is taking legal action against Berkshire Bed Company, trading as Beds Are Uzzz, which supplied it.
The firm denies liability for Ms Busby's injuries, arguing the bed was properly assembled.
Neil Block QC, for the firm, said: "It is overwhelmingly likely that, whatever her actions, they were too close to the edge of the bed and she simply lost balance and toppled backwards".
The hearing continues.