Pascal's character, Joel, broke down to his brother about his fear of losing Ellie (Bella Ramsey) and told him that he has heart-stopping dreams every night that wake him up.
When asked what the dreams are about, Joel admits he doesn't know. "I can't remember," Joel says. "I just know that when I wake up, I've lost something. I'm failing in my sleep."
The exchange may be short, but for reticent, traumatized Joel, it's a huge show of vulnerability – one that reframes his entire character. And apparently, part of it came from Pascal himself.
Mazin paraphrases that "the [lines], 'I have dreams ... All I know is that when I wake up, I know I've lost something,' that was something from Pedro directly."