The 46-year-old actress has won rave reviews for her performance in 'A Streetcar Named Desire' at London's Young Vic theater but had to seek specialist help before her run started after suffering panic attacks brought on by a fear of forgetting her lines.
She said: "I was terrified because I've had panic attacks on stage before so deciding to do this was a lot of pressure.
"I went to a couple of different hypnotists to deal with the anxiety because about six months before I started I was already projecting the fear of the future onto really small moments and struggling to even give a thank you speech.
"I think the combination of hypnotherapy and working my a*s off so that I was comfortable with the material meant that it hasn't been an issue."
Gillian - who has children Piper, 20, Oscar, eight, and Felix, six, from previous relationships - has previously suffered from panic attacks so bad that she "hallucinated".
She recalled in an interview with Stylist magazine: "There was a period of time when I was pregnant with my daughter where I started having panic attacks and they pretty much happened every day for well over a year.
"And it was absolute hell - like hallucinatory - really bad."