The email, in which Ortega said the singer was in frail mental health, was shown to the jury Monday. It was sent to Randy Phillips, head of the company promoting Jackson's London concerts, five days before Jackson died in 2009.
Ortega wrote "trouble at the front" in the email's subject line.
"There are strong signs of paranoia, anxiety and obsessive-like behavior," Ortega wrote. "I think the very best thing we can do is get a top psychiatrist in to evaluate him ASAP. I honestly felt if I had encouraged or allowed him on stage last night he could have hurt himself. I believe we need professional guidance in this matter."
Testimony Monday in the wrongful-death lawsuit Jackson's mother and three children have filed against Anschutz Entertainment Group also revealed Ortega didn't have a contract, just a series of emails.
It was revealed earlier that Dr. Conrad Murray, who administered the fatal dose of the anesthetic propofol to Jackson, did not have a signed contract with the promoter of the London concerts by the singer, who died two weeks before they were scheduled to begin.
As Murray, who worked with the singer for two months to prepare him for the concerts, signed his contract the night before Jackson died, but neither the singer nor a company executive signed.
"And Dr. Murray had an agreement with AEG based on a series of emails?" Panish asked.
"No. I don't believe so," Trell replied.
Asked why Ortega didn't need a contract, Trell said, "Kenny Ortega is different."
Panish showed the jury a series of emails between Murray and AEG executives, including one dated May 8, 2009, in which AEG's Paul Gongaware agreed to pay the doctor $150,000 a month. Jackson died June 25, 2009.
In another email, tour accountant Timm Woolley went over details of employment with Murray, including a provision that if he didn't travel on Jackson's chartered plane, he would fly first class.
In a May 22, 2009, email, Murray wrote to Woolley that he was faxing over a voided check so that money could be wired directly to his account.
When Panish insisted that Murray was working for AEG in May 2009, Trell replied: "No. I totally disagree with that statement."
The Jacksons' lawsuit contends that AEG "hired and controlled" Murray, while the entertainment giant argues that any money it was supposed to pay Murray was an advance to Jackson, who hired the doctor.
Previous testimony has shown that Murray was never paid. On Monday, Trell was shown a report that AEG sent to Michael Jackson's estate that included a request that it be repaid $300,000 it had given Murray.
"To me, it's a mistake," Trell said.