A winner of TV's Who Wants To Be A Millionaire? quiz turned on a researcher minutes after scooping the top prize, a court has heard.
Mr and Mrs Ingram deny the charges
The prosecution claims Major Charles Ingram, 39, scooped the gameshow's £1m jackpot after lecturer Tecwen Whittock, 53, signalled the correct answers by coughing at the right moment.
Researcher Eve Winstanley told Southwark Crown Court Mr Ingram seemed very "unhappy" for someone who had just won a £1m.
When she offered him a drink in his dressing room, he refused, saying he had to work the following day.
I had never been spoken to by a contestant like that before
Researcher Eve Winstanley
The major and his wife Diana, 39, from Easterton in Devizes, Wiltshire, both deny conspiracy to "dishonestly procure the execution of a valuable security" in September 2001.
Mr Whittock, of Whitchurch, Cardiff, who is head of business studies at Pontypridd College, denies the same charge.
Ms Winstanley said of the couple: "They didn't seem happy or anything else really.
"Mrs Ingram seemed a little bit agitated and Mr Ingram seemed a little bit tense."
Tecwen Whittock is also accused
When she said to Mr Ingram she would not have expected a £1m winner to be going back to work, he raised his arms in the air and said "you don't understand".
He told her to get out and she heard the sound of arguing.
When she returned to the room his wife seemed "shaken and upset".
"I had never been spoken to by a contestant like that before," said Miss Winstanley.
Earlier the court had heard Mr Ingram, an officer in the Royal Engineers, had seemed "politely surprised" when told his £1m prize was being withheld.
Mr Ingram reacted "very calmly" to the news his prize money was being stopped pending an investigation, according to Paul Smith, managing director of Celador productions.
Asked if publicity generated by the trial would boost the programme's ratings, Mr Smith said Celador planned a programme about the major's appearance on the show that would have "curiosity value."
The prosecution said Mr Whittock, the alleged "cougher" was one of show's "fastest finger first" contestants who was sitting near to the major.
Prosecutor Nicholas Hilliard suggested the Ingrams may have considered using a system of vibrating pagers to indicate the right answers on the first evening of competing before deciding the coded coughing offered a better chance of winning.
Ms Winstanley said she had first met Mr Ingram when he got as far as winning £4,000 on that first night.
Mrs Ingram's brother Marcus Powell had asked to sit in a VIP "overspill" area, she told the jury of eight women and four men.
She had twice seen him outside the studio on a mobile phone and had told her production supervisor and security staff.
Celador decided not to broadcast the show and contacted police.
The trial restarted on Friday after a juror fell ill.
Mr Ingram has launched civil proceedings to recover the £1m.
The trial continues.