The title explains it pretty well; I woke up this morning to find that one of my zebra finches died, leaving me with just one finch. I noticed how unusually quiet it was this morning without their usual 'beep-beeps', and singing. One was missing, so I removed the nest, and in there was the deceased finch, contorted in an odd position with his tail straight up and his head swung back. He hadn't gotten tangled up in any nest material, because it was easy to roll him out of the nest for examination, and he hadn't shown any signs of illness just yesterday. The sudden death itself is concerning, of course; but what I'm really worried about is that my other finch seems rather sluggish, and is sleeping a lot. It's only 9:26 in the morning and he's asleep. He had a nice meal this morning despite this, and hopped around and flew to and fro like a normal finch, but after about five minutes of watching him behave normally, he promptly went to his perch and went to sleep.