Liev Schreiber is opening up about a terrifying experience he had while acting in a play.

During a recent appearance on "Late Night with Seth Meyers," Schreiber detailed the neurological disorder he experienced prior to going on stage to perform his role in the Broadway production of "Doubt: A Parable."

"The worst nightmare that an actor could possibly ever experience," he told host Seth Meyers. "I was in my dressing room, and I had a terrible headache. I thought it was maybe a fast-food headache, but it felt a little stronger than that. I’m walking down the stairs, and I’m thinking, ‘This is not normal. I don’t feel OK.’"

He said he "knew something was really wrong" when he ran into his co-star, Amy Ryan, backstage but couldn't remember her name or common phrases actors say to one another, like "break a leg," even though he has "said it at least 30 times by that point."

Liev Schreiber on the red carpet for his Broadway play

Schreiber experienced amnesia during one of his performances in "Doubt: A Parable." ( Bruce Glikas/WireImage)

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Schreiber recalled telling the stage manager something wasn't right with him, but the manager quickly called places and the play began.

"So, I go on, and I do about the first six or seven lines of the play, sort of automatically. I realize I'm not connected, so I decide, let me try and get connected again. And the minute I do that, it all vanishes. The play is gone from my head," he explained. "I'm looking out into a dark audience. I know I'm in a play, but I don't know what play I'm in. I look down at my clothes, and I realize I'm a priest, which is helpful, but not giving me any lines." 

After getting off stage and rushing to his dressing room, he recalled seeing his friend who is a doctor and his wife looking at him with "a terrified expression," leading him to think, "OK, I’ve had a stroke. This is it."

"I go get the MRI, no brain bleed. Perfectly fine," he explained. "I find out ultimately from a neurologist I had something called transient global amnesia, and, apparently, my wife looked it up online. It's brought on by migraines and rigorous coitus."

Liev Schreiber and Amy Ryan on stage performing

Schreiber found out he had transient global amnesia. (Bruce Glikas/WireImage)

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According to Cedars-Sinai, TGA is described as a sudden loss of short-term memory, which typically lasts no longer than 24 hours. There isn't one specific cause of TGA, but it has been associated with migraines, sexual intercourse, sudden exposure to hot or cold water, emotional stress and mild head trauma. 

The "Ray Donovan" actor said he didn't believe doctors when they told him his symptoms will "be gone in eight to 24 hours," joking that "as a typical sort of Jewish hypochondriac person," he was fully "convinced that [he] had a stroke, and they just didn't find it."

"I go to sleep, I wake up, I remember the whole play. I call the theater and I say, ‘I’m coming up to do the matinee. And they're like, ‘No, no, no. Your doctor said you have to stay away until Tuesday.’ And I was like, ‘No, I need to know that I can do the play,’" he said on "Late Night with Seth Meyers." 

"I never had another problem with it. I was embarrassed and thought everyone would think I was lying and taking a night off from the theater."   

Schreiber added that, of all the ways to get TGA, he "had to get it from a migraine," joking with Meyers it was a bummer "when the other option is to literally have your brains f---ed out."

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Liev Schreiber on stage with the cast of "Doubt"

Fans can see Schreiber in "Doubt: A Parable" until April 21. (Bruce Glikas/WireImage)

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"Doubt: A Parable" opened on Broadway in March with a closing date of April 21.