When a dog shows a sudden change of behaviour, it can be a cry for help. 
Behaviour that can sometimes appear to humans as ‘naughty’ or ‘out of the blue’  can be your dog trying to let you know that something is wrong.

If your dog has displayed a sudden, unexpected change in behaviour then I will usually ask you arrange a vet check for them as a first step.  Dogs can hide pain extremely well and it can result in them behaving unusually due to an injury or illness.  It is important to find out if there are any medical issues which could be causing your dog's behaviour change before embarking on a behaviour reformation programme.  I am happy to work in conjunction with your vets.