AceShowbiz - Justin Theroux had temporary amnesia and was warned he'd need brain surgery following a skateboarding accident.

The 49-year-old actor confirmed a story about him being hit by a van while out in New York City and told how he couldn't remember his name when he eventually woke up after being knocked out for "a long time."

He recalled on "The Ellen DeGeneres Show", "(There were) people all around me. I clearly blacked out for, I think, a long time. There was a woman over me weeping (and) there were two men holding my arms so I wouldn't touch my head."

"The woman was screaming at me, 'Who are you? What's your name? What's your phone number?' trying to get in touch with someone."

"It was as if someone had asked me 'What is an umbrella?' and I forgot the name of umbrella, but it was myself. I had no clue who I was. I mean, I knew I was me, but I couldn't remember my name and I couldn't remember my phone number."

"The Leftovers" actor had to wait over an hour for an ambulance to come, and was told by medics they would have arrived more quickly - but they thought he was dead.

He continued, "This is kind of the New York hilarious part of it: the ambulance took about an hour and 20 minutes to get there. I was lying on the pavement and people are now kinda getting bored with this guy with blood pouring out of his head."

"Finally the EMT shows up over me … He turns back to his partner, who I guess was still back in the truck, and he goes, 'He's not dead.' "

"(They told me they would have been) quicker if we knew you were still alive."

And things got "worse" when Justin was admitted to hospital overnight for observation as he was roused from sleep to be told he needed brain surgery and had to be prepared for the operation.

He said, "It got worse. I had a concussion. Then I went into the hospital that night and they had to keep me overnight for observation; they gave me all these brain scans and things. … A guy wakes me up in the middle of the night and he says, 'We gotta get the doctor in here from Jersey, we think we noticed something on your CAT scan.' "

"It's like two in the morning. Then they shaved my head and prepped me for brain surgery."

"I go, 'Oh, okay.' Then they make you sign all this paperwork and I'm thinking like, 'I gotta call somebody! There's no one to call!' So, I sign my life away on these papers, then the doctor finally gets there from Jersey, and he comes in, sort of rumpled hair, and he looks at the CAT scan and he's like, 'This a thing with the scan, it's not blood on the brain. Go back to bed.' "

"I spent about half an hour waiting just to go to brain surgery, but it was nothing."

"I had a nice big bald patch in my head. Couple stitches and I was discharged in the morning."