The trial resumes on Monday in the Federal Court in Sydney, where Mr McGowan and WA Attorney-General John Quigley will appear in person.
Mr Palmer is suing Mr McGowan, claiming public comments - including labelling the Queensland businessman the "enemy of the state" - had damaged his reputation.
The premier has lodged a counter-claim that the billionaire defamed him in several interviews and statements.
The comments by both men were made in mid-2020, around the time Mr Palmer and his company Mineralogy launched a failed bid in the High Court to have WA's hard border declared unconstitutional.
Further background to the case relates to the McGowan government introducing extraordinary legislation which prevented Mr Palmer and Mineralogy from suing the state for billions of dollars over the Balmoral South iron ore project.
In his evidence last month, Mr Palmer said he was "scared" because provisions in the legislation protected the government from criminal prosecution.
His look at the law indicated "they could really do anything to me".
Referring to the fictional character James Bond and his "licence to kill", Mr Palmer told the court: "I didn't know what the limits might be."
"I was just scared because I didn't expect governments ever to produce legislation like that in Australia so it really told me that you'd better take these people seriously, they could do anything."
Asked by Justice Michael Lee whether he had a genuine fear for his physical safety, Mr Palmer said it was not just for himself, but his employees in WA.
Mr McGowan's barrister Bret Walker SC suggested Mr Palmer had a "marked and reckless willingness to say terrible things" about the premier.
But Mr Palmer said comments he made about Mr McGowan's relationship with China were factual.
He acknowledged some statements were levelled in retaliation but said others were fair political comment and not intended to be personally offensive.
Attacks by Mr McGowan left him upset and unable to sleep at night.
The premier has insisted he will quarantine for a week upon returning to WA, despite the hard border having been lifted this week.
He said it was necessary to dispel any argument that the reopening date was put in place to benefit himself.
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