Thank you for getting back to me. I apologize for the delay - we are dealing with a large time zone difference since you are in Australia and I am in the States. We'll just have to work around the delays that causes.
The symptoms you're seeing do not sound like a normal slowing down. Vomiting is never normal, and weight loss is cause for concern. You are suspicious of a blockage, and based on what you have described, so am I. Classic symptoms include appetite loss, vomiting, and passing no or watery droppings. Watery droppings can get past a partial blockage, while more normal ones can't. As for the head movements and mouth opening, that can signify some discomfort in the throat or mouth, or difficulty breathing.
There is no way to be certain of what is going on without a hands on exam and x-ray. He may have accidentally swallowed some substrate or some food may have caused an impaction. He may have an infection or parasites causing the symptoms. Because of these possibilities, I recommend that you see a reptile vet for a certain diagnosis and proper treatment. These links will take you to directories of Australian reptile vets:
If you have more questions, let me know in a REPLY. I hope this will turn out to be something easily treated.
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