The reasons why dogs curl up to sleep:

1. The temperature of the living environment is too low, and the dog is too cold and makes special movements to keep warm.

2. If the dog is uncomfortable with pain caused by some reason, curling up the dog can help relieve the pain.

3. Dogs take self-protective measures when they are in a strange environment or are beaten and scolded.

Solutions to dogs curling up to sleep:

1. If it is caused by cold, the owner should take measures to keep warm, such as turning on the air conditioner and adding an electric heating pad.

2. If it is caused by pain, the owner should take it to the hospital for treatment in time.

3. If it is caused by the dog being afraid, the owner should spend more time with the dog to calm the dog's mood.