The businessman made the comments during cross-examination at the East London Employment Tribunal Service earlier today, following English's claims of constructive dismissal.
She says her £100,000-a-year job at Sugar's Viglen division was "a sham", adding that she was eventually forced to resign from another post at the business when Sugar refused to renew her contract.
"I began to think that perhaps the reality of work rather than the glamour of showbusiness was beginning to bite with her," Sugar said. "Her time in the limelight was beginning to fade.
"In hindsight, I can now see that she was a very untrusting and suspicious person. It was clear to me now that she thought that everyone was out to trick her.
"She thought during the whole [Apprentice] process that she was being lied to and that the other candidate has been chosen as the winner.
"She always came across as quite reserved and detached and, some might argue, cold. At other times she would come to me with some very odd conspiracy theories."
Sugar said that English confronted him during her four-month probation period with the idea that eventual runner-up Chris Bates had won the competition since she hadn't yet been filmed leaving his office in a chauffeur-driven car.
Both candidates had worked for Sugar in 2010 before he made his final decision. She is also said to have accused his PR agency of leaking information about her family to the press.
Meanwhile, English claimed to the tribunal that Sugar had told her: "I did it for the BBC and the integrity of the show and a bit of my own PR and a bit of yours too. But the fact is that I don't give a s**t."