Hi, My little "Bruiser" has done that before. He is a short haired Chihuahua, very cold natured, and will even stay under his blanket in the summer. However, there have been a few times when he was "shaking" pretty bad. It was his stomach bothering him? I always give him a snack at night, this really seems to keep his "blood sugar" level and does help with the shaking. (he hates ceiling fans)
bruisersmom