"I was two blocks from my house when the car hit my side, the passenger door," the actress, 37, told PEOPLE at the Cinema Society screening of Conviction hosted by Laura Mercier on Tuesday. "The good news is that I was feeling sleepy and leaning in. So, that saved me from more brutal injuries."
She added: "I didn't actually smash my head. I just got jerked violently."
Lewis could walk after the accident, but the emergency responders encouraged her to seek treatment. "The paramedic said to me, 'Juliette, you don't understand. We don't normally see people walk away from a crash that bad … You need to go to the hospital,' " she said. "He had to convince me."
Asked if the experience was terrifying, the actress replied: "I can't even go into it, it's so sad. I'm still a bit shaken up."
Lewis revealed that she once lost a friend in a car accident. "It's one of those things that reminds you," she said. "It reminds you to focus on the little things, the good things. Right afterward, I got together with my friends and family. I was touched to see everybody."
The actress is now doing physical therapy for whiplash, and reflecting on the lessons learned from such a close call. "Live in the here and now, live in the journey," she said. "All of that good stuff."