Just rescued a feeder yesterday to wake up to it dead. He kept running around last night and I just figured he was figuring out his new home?

Quetzel

If you're talking about a mouse, it could have been anything. Did you leave food and water? The feeder rat I recently saved was ready to die when I got him. He was very skinny, extremely dehydrated, hunch backed, coarse, clumpy fur, dull eyes. He was just a feeder, the snake owner didn't care if he was healthy.