Thanks for that. Given he is such a big boy (even with the weight loss), if this was a normal chocolate brownie with no icing, then this wouldn't have caused him any issue. While chocolate is toxic to dogs, it does depend on the type of chocolate, the amount ingested and the size of the dog. Symptoms of chocolate toxicity are also the opposite of what you are seeing: hyperexcitability, restlessness, increased urination and thirst. So - there is definitely something else going on here with Jake, and we need to consider everything from a musculoskeletal issue (such as arthritis), to an internal organ or endocrine problem, to something else entirely. If he is particularly lethargic right now, then there is no question that you really do need to get him seen by your local vet this afternoon if you can.
In the meantime, please keep a close eye on Jake's mucus membranes, capillary refill time and respiratory rate as follows:
Mucus membranes - flip his lip and look at the color of his gums. They should maintain a nice salmon pink color. Get him to the vet if they appear white or very pale pink, or if they are a dark deep red color.
Capillary Refill time - this measures blood perfusion and test this by putting your thumb on his gum to apply pressure. After you release your thumb you will see the gum blanch. Capillary refill time is the amount of time it takes (in seconds) for the gum to return to a healthy pink color from the blanched white color. If 2 seconds or less don't worry - if it is taking significantly more time, again - off to the vet.
Respiratory Rate - if he is continuously panting throughout the afternoon, this is a sign of shock and or pain and a signal for a trip to the vet.
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