I apologize that no one has responded to your question sooner. Different experts come online at various times. I just came online and saw your question. My name is XXXXX XXXXX I'm a biologist with a special interest in birds. I'm so sorry for the loss of your other parakeet.
Birds do grieve for the loss of their companions, but the symptoms your bird is exhibiting indicate Angel is probably sick. It could even be a combination of factors, with grief leading to a depressed immune system and illness. Not having normal energy levels, sleeping a lot, and being cold only tell us that something is wrong, without letting us know what it is. They are general symptoms. Birds tend to hide signs of illness, so by the time symptoms like you're seeing show up, the bird is often quite ill. I recommend that you take Angel to a vet. The symptoms you're seeing can indicate anything from a respiratory infection to organ failure to cancer. For all these reasons, it would be good to have Angel examined by a vet. A vet who is experienced with birds would be best. Here is a site that will help you find one near you:http://www.avianweb.com/recommendedvets.htm
In the meantime, make sure he is kept warm. If there's a warmer room in the house where you can move the cage to, that would be a good thing to do. You could also cover three sides and the top of the cage to keep warmth in. Another option is to use a clean sock, and fill it 2/3 with plain, raw white rice. Tie the open end and microwave it for about 1 1/2 minutes. Then shake to distribute the heat. Make sure it's not so hot that it could burn your bird. Put it in the cage for added warmth. You can re-warm it when it gets cool. Angel can stay near it if he's a bit chilly, and move away if he gets too warm.
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