Cats and dogs have done that before too. And it's scary. Sometimes it doesn't even relate to sleep. I remember I had a bracelet as a collar for my cat. I woke up in the middle of the night and I saw him laying on the floor. Sometimes he likes to flop down when he's in a hyper mood, then he'll start playing with whatever is on the ground. Anywho, I noticed he tried walking, but whenever he did, his wrist just failed and he laid back down. I thought he fell off the chair and somehow broke his paw. But it turns out, his arm was just stuck in the bracelet, I had to cut the bracelet off since I couldn't get his arm out. Nearly gave me a heart attack