Why does my gerbil freeze up when I hold him? :(?

I will pick him up all fine and he's fine with me for like a minute, but then his whiskers twitch and he closes his eyes and he freezes up and literally acts like he's dying or having a seizure!! Then when I put him back into his cage, I let him gently and I rub his ears and he soon like snaps out of it. I'm so scared. Today he did that and when I went to put him back into his cage, he rolled off my hand onto the carpet :,( he doesn't move. He's just like stiff. He's all fine right now in his cage but WHY DOES THAT HAPPEN??? I'm so scared for him. He's my little baby :,( Pet* him gently....not let