I was assigned to nurse the captured victors back to health, and we were expecting what we saw with the girls - heavily bruised bodies, obvious evidence of rape and the of course Johanna Mason had the burnt skin showing electrocution. Peeta Mellark, however, was in surprisingly good shape. His ribs were cracked, I'm guessing from his beating after he warned District 13. But aside from slight bruising, it seemed like they hadn't been beating him recently at least. I figured they were getting him ready for another interview when we rescued him.
But then the Mockingjay entered.
I was one of the doctors he'd pushed out of his way, hitting my head against the wall with the force. But before my vision blacked out, I saw soldier Boggs prying his hands from the neck of the girl. The girl he told us he loved. Later, I entered the information into his log.
Peeta Mellark: 47th known victim of hijacking.

He didn't know where he was. Nobody told him, they just assumed he knew. He wasn't in the Capitol, he was semi-conscious for part of the hovercraft flight, and they were flying far too long to still be there. He couldn't muster up the energy to fight as the doctors checked his vitals and injected him with who knows what.
Then he heard something behind him, someone come in and whisper his name. He turned his head slowly. He recognized that voice.
She came for him, arms outstretched, a terrifying expression on her reptilian face. Her fangs dripped with the blood of those she'd killed. He had no choice. This isn't Katniss. This is the creature from the Capitol. Katniss would want him to kill this mutt. He felt his hands close around that scaly throat and squeezed with all the strength left in him. He wouldn't let go until this monster was dead.
He felt a blow to his head, and with a rush of pictures and sounds, everything in the room lightened from grey to white, bringing him violently back to the room he'd been beaten so frequently in.
He curled up and wrapped his arms over his head, a reflex he'd developed from years of abuse from his mother, as well as from his days of constant beatings in between torture sessions. He whimpered as a hand gently rested on his arm and pierced the skin there. Emptiness followed.

He had woken up several times in the days following his encounter with the Katniss-beast. His doctors and nurses kept assuring him he was safe, they were there to help, and Katniss wasn't a mutt and she was fine. He didn't really believe any of it.
"Peeta? Are you okay?" The nurse asked.
"Yeah."
"Do you know where you are?"
"District 13."
"Would you like to take a rest, we will give you something."
"No, I want to... Try..."
"Peeta?"
"Where am I? Who are you!"
"I'm your nurse. You're in District 13, you knew that a second ago."
"Don't sedate me, I don't want to be like the morphling that... No! Don't die for me, I don't deserve to live! I-I'm not supposed to survive this ti- Please don't me don't kick me again! No, I can't stop her, she's gone, I can't..."
"Peeta, you're okay, you're safe in 13. Nobody's hurting you."
"Fog-fog, Mags don't go! The fog..."
"Peeta? Can you hear me?"
"No, don't take her away from me! I love her. Don't take her from me! Kat-Katniss I'll always remember you, I'll always love you, they can't take that!"
Peeta's cries dissolved into choking sobs as the doctor smoothed back his hair, apologized, and inserted a needle into his arm. It's imaginable that each time he was freshly disoriented, it was linked to something the doctor had said that coincided with what his torturers had said.
It was six hours before the medication wore off, and Peeta was alert once more. Each time he woke up, he reached out for Katniss, as he'd grown so used to doing. And each time, his hands met with empty air. The nurse would come in with food and refill his IV. One day he asked what she was putting into him, and she told him it was a mild sedative to help him stay calm.

"You're lying." He told her. "You're lying, it's more venom, you're trying to change me into a mutt like you did to her."

"No, Peeta, that was what they did in the Capitol, but we rescued you. We're trying to make you better here."

"Why should I believe you?"

"I guess for now, you'll have to trust me."
Trust me. Trust me. Trust me. His arms tightened automatically and a growl came from his throat. The nurse looked scared and started to back away slowly. Peeta started shaking violently.
"She won't eat them too, she'll trick me so I die by myself! Don't eat the stupid berries! She's a liar, a dirty rotten liar! Don't trust her, I did and look at me now!"

"There's no berries, Peeta, it's just stew, it's perfectly fine. Nobody wants you to die."

"That's what she told you, isn't it? The Capitol turned her into this, this is the Capitol's fault! I'm going to die by myself while she wins the Games alone, she just kept me along for the sponsors. I thought she loved me but really it was all one big Game to her. She's a liar, woman! She's a liar!"

Once more, the nurse injected him with morphling to put him to sleep.