"'I love you, mama. You're the best,'" Lisa recalled Angus telling her in a Sept. 25 interview with People. "'I'll see you in the morning.'"
Her son gave her a hug before she went to bed that night, according to Lisa. But by the morning, Angus had passed.
"I started shaking him and screaming," the mom recalled of the next morning. "I pushed him hard, and he fell on the floor. I tried to resuscitate him—mouth to mouth—and I was compressing him."
She continued, "I was screaming for my neighbor because I didn't want to leave him and call 911, and I just kept at it until they took him away."
According to Lisa, not a day goes by that she doesn't think of her son.
"I miss him so much," she said, wiping away the tears. "He was the love of my life."
Earlier this month, the Alameda County Coroner confirmed to E! News that Angus' cause of death was determined to be a result of a lethal combination of fentanyl, cocaine, methamphetamine and other substances.
Lisa noted that the North Hollywood actor was heartbroken over his father Conor Hickey's death in May and she could see that he had a difficult time coping with the loss. However, she firmly believes that Angus—who passed away just one week after his father was laid to rest—didn't mean end his life.
"It was predominantly the central nervous system depressants," she explained to People. "It started to slow his heart and slow his breathing. He got tired from lack of oxygen. Everything just slowed down, and eventually his heart stopped and he went to sleep."
She added, "But he didn't kill himself."
Though Lisa is still grieving the loss of her son, she explained that the overwhelming support from fans has helped her cope.
"He went out at his total power, his total beauty, his total influence, and the reaction that everyone has had is very moving to me," she said. "You know, he's not just an actor who overdosed. He was a beautiful soul, and that's why people miss him so much."
If anything, Angus' mom felt in her heart that he'd leave an indelible mark.
"I always knew he was special and I'm so glad the world also found out he was special," she shared. "My son will always shine bright."