Why was my dog acting like this?

today when i came home from school my dog started out acting normal, he wanted his routine treat that i give him wen i come home. About 2 mins later i heard whining in our basement so i went downstairs to find him laying on the concrete in a corner in our basement. our basement is being finished Right now so its all concrete, but my dog NEVER lays on concrete always on a rug. when i went over to him he was shaking and look petrified almost like he had seen a ghost. he wasn't injured and he was walking fine but he kept looking around nervously and he looked terrified. i tried to get him to come upstairs but he wouldn't budge not even for a treat! **btw my dog never goes in the basement in the first place he hates it down there. what would have caused him to do this?