Jurors heard evidence of further instances of violence between the couple as Ms Heard continued her evidence on Monday, including an alleged “prank” involving faecal matter being left on a bed at one of Mr Depp’s properties.
Mr Depp is suing the Aquaman star for libel over a 2018 article she wrote in The Washington Post which his lawyers say falsely implies he physically and sexually abused her while they were together.
He has denied all accusations.
Asked about her decision to file for divorce from Mr Depp in May 2016, Ms Heard replied: “I knew if I didn’t I’d likely not literally survive.
“I was so scared that it was going to end really badly for me and I really didn’t want to leave him, I loved him so much.
“I would have done anything but I couldn’t do that one thing, I couldn’t stay.”
She continued: “The promise and the hope I had became less and less regular and more and more rare.
“The monster was now the thing that was normal and not the exception. The violence was now normal and not the exception.
“It was so hard but I knew I had to do it… what if he had taken it too far, I wouldn’t be here.”
The actress also told the court how she had been desperate for a “good night’s sleep” and repeatedly asked members of Mr Depp’s security team not to let him into the property while she was there overnight.
She said her anxiety had caused her to lose hair and weight and have regular panic attacks.
Ms Heard also denied involvement in an alleged “prank” involving faecal matter that caused Mr Depp to become enraged and physically violent.
She said the actor had become “delusional” when asked about the incident, which happened in April 2016, shortly after her 30th birthday.
The court heard Mr Depp had discovered faecal matter on a bed at one of his properties in Los Angeles and had called Ms Heard about the matter.
“I don’t think that’s funny, I don’t know what grown woman does. I was also not in a pranking mood,” Ms Heard said.
“My life was falling apart.
“I was at a crossroads in my life. I’d just been attacked on my 30th birthday by my violent husband, with whom I was desperately in love and who I needed to leave.
“It was not really a jovial time and I don’t think that’s funny. Period. That’s disgusting.”
The court heard a suggestion that the faecal matter had come from Mr Depp’s Yorkshire terrier Boo, which had “bowel control issues” after ingesting some of the actor’s marijuana as a puppy.
Ms Heard said that after confronting her about the incident in person, Mr Depp had screamed abuse at her and become physical, causing her friend, Raquel Pennington, to come between them and the actor’s security guards to intervene.
She added that as he left the apartment Mr Depp had taken a bottle and smashed several items, and that the police had been called.
Concluding her direct evidence, Ms Heard said that toward the end of their relationship violence had become “almost normal” and detailed further alleged instances.
The jury was shown red carpet photographs in which Ms Heard appeared to have marks on her arms, which she said were scars caused by Mr Depp.
Audio recordings were also played in which verbal altercations between the couple could be heard.
Mr Depp has refused to make eye contact with Ms Heard during the three days she has been giving evidence.
Long queues continued to appear outside Fairfax County district courthouse, in Virginia, with some members of the public having queued overnight for a chance to get into the courtroom to observe the proceedings.
Mr Depp has already given evidence and faced cross-examination and has alleged that he was a victim of domestic abuse during the relationship.
The trial continues.