Your dog might be having seizures. I would get him to the vet asap. Be prepare to describe what he is doing and how often it occurs. They will also want to know if he looses consciousness and if he drools or wets himself. The vet will also want to know how long they last and how he acts afterward.
If it's like a seizure he needs to get to the vet, and he should be seen anyway if it's not just when he's excited or something. Best wishes
Perhaps this is a part of the dogs make up, as some dogs do shake like they are freezing cold all the time but it is just a part of the breed, they just naturally shake, there is no real reason......the best to you, it would be helpful if you would read up on the breed and find out more about them.....the best to you
Smaller dogs will shake more than larger dogs, as they loose a lot of body heat
Well mine does that when she is scared and when she is cold she also does that when she is tired.