Sorry to hear Ice is feeling unwell, however I have worked out an answer for you below ...
1. Having read your question through I have to say that if these symptoms continue then what you should do just to be on the safe side is have a vet check Ice over sooner rather than later. The reason I say this is that while the symptoms you describe would not allow me or any other vet to pin this down to any one particular disease via the internet the fact that he is suddenly lethargic and shaky makes me think that it is possible that your dog is running a temperature and so may be in the grip of some kind of infection. This would be the commonest cause of what you are seeing although of course other diagnosis are also possible particularly in a dog of thirteen years of age.
2. I normally like to suggest home remedies if I can do this safely but in your case I think it is not worth the risk as it could well be that prescription drugs such as antibiotics would be what is needed if he is indeed running a temperature. In the meantime until you can get your dog to a vet all you can do is to keep him comfortable and reassured and make sure he is taking fluids regularly.
3. However I should be available online for you the next four or five hours today so please do not hesitate to get straight back to me if Ice's condition changes in any way or you would like to talk things over with me further.
I am sorry I cannot safely give you any more specific advice via the internet.
I hope I have covered your question fully enough but if you would like further clarification or to talk things over a bit more then I will be on-line for the next hour or so and I will be more than pleased to continue working with you.
Please be kind enough to rate my service to you after we have concluded our dialogue, such feedback helps me maintain the quality of my answers.