In Avengers: Infinity War, Thanos’s finger snapping caused him to wipe out half of the universe. And in Avengers: Endgame, when the Avengers got all the Infinity Stones from the past, Hulk put the Gauntlet and snapped to bring all the vanished people back.
But do they know what happened to them in the last 5 years?
Well, we don't know exactly, but it seems they don't know what happened. They seem to think they were passed out during that period. When Peter hugged Tony Stark, we can see him mentioning that last time he was dusted he must have been passed out.
Peter: Do you remember when we were in space? And I got all dusty? I must've passed out, 'cause I woke up, and you were gone.
Peter: But Doctor Strange was there, right? He was like, "It's been five years. Come on, they need us!"
It seems they don't remember anything after they were dusted.
As Director Joe Russo explains,
As for Peter Parker and those who got dusted, they were basically taking a nap in which no one ages. "To those dusted people, they had no conscious in these past 5 years," Joe Russo went on. "They didn't know what happened. It's as if they had just woke up from a long sleep. The only one who was aware about how many years has passed was Doctor Strange, because he has already seen that when he was time mediating on Titan.
No, the vanished people were completely unaware of what happened to them or the world in the last five years. For them, it felt like they blinked and woke up in a different time. The MCU gives us several examples of how disorienting and traumatic this experience was for the people who returned.
One example is Yelena Belova, whose point of view we see in Hawkeye season 1, episode 5. She was in a bathroom when she suddenly turned to dust and then returned from being dust, seemingly in an instant. She had no idea that she had been gone for five years, and that her sister Natasha had sacrificed herself to undo Thanos’ snap.
Relevant dialogue:
Yelena: Ana, I was in there for five seconds, I come out and I've lost five years of my life. Please.
Another example is Monica Rambeau, who we see in WandaVision season 1, episode 4. She was at the hospital with her mother, Maria, who had just survived a procedure for cancer treatment. Monica fell asleep in her mother’s room, and when she woke up, she was surrounded by chaos and confusion. She learned that she had been missing for five years, and that her mother had died three years ago from a cancer relapse.
Relevant dialogue:
Dr. Highland: Monica?
Monica: Oh, Dr. Highland, thank God!
Dr. Highland: I can't believe it.
Monica: (STUTTERS) Uh, I was...
Dr. Highland: Where did you go?
Monica: Well, in her room since she came back from the surgery. I mean, I might've have fallen asleep, but no longer than 20 minutes. Dr. Highland, where's my mom?
Dr. Highland: Your mom, she died, honey.
Monica: What? No. No, no, no, no, you're mistaken. My mother... The procedure went well. You said so yourself. Clean margins. You're discharging her today.
Dr. Highland: The cancer came back.
Monica: Okay, stop, stop. No, you're... My mom is Maria Rambeau. Look it up. I mean... Look it up. "Maria Rambeau."
Dr. Highland: Monica, I don't understand what's happening, but you need to listen to me. Maria died three years ago.
Monica: Three? No. No. No, no...
Dr. Highland: Which was two years after you...
Monica: After I what? After I what?
Dr. Highland: After you disappeared.
This scene clearly shows how confused and shocked Monica was by the fact that she had missed five years of her life and that her mother was gone.
But do they know what happened to them in the last 5 years?
Well, nothing happened to them in the last 5 years, and they are aware of nothing, so technically the answer is "Yes".
