Thrashing/Flailing Limbs

My son will be 3 weeks old tomorrow. In thr last day or two, he has started thrashing his limbs around and grunting when in the active sleep cycle. This is different from his startle reflex, which is strong. He gets the rapid eye movement, his arms move around all over the place, sometimes hitting him in the face, his legs kick about. It is unsettling. If he can manage to get through it without eaking himself, he can get into the quiet sleep phase.

Just wondering if anyone else is experiencing this or has experienced it? We do swaddle, but his littlr arms fight so hard to break through it, I feel bad. 🙁