Thank you for your patience. Scouts symptoms are definitely quite a concern, and it is a worry if he is unusually lethargic this evening. There are a range of things that could be going on her with your boy including anything from early gastroenteritis, to a toxicity or poisoning (hopefully there isn't anything around your home or yard he could have gotten into), or even an internal organ issue or endocrine problem. You are going to need to continue to keep a close eye on him. If he seems particularly bloated, then there is even a risk this could be a GDV - a stomach twist and bloat. If he seems particularly bloated, then you are best to play it safe and get him seen now if you can.
For now, in case he does have some GI upset, you can with hold his food until the morning, but make sure he has plenty of fresh water available and do encourage him to drink. You may also want to try him with a little pepcid. The typical dose for this type of situation is 0.25mg per pound of body weight up to twice daily. You can read more about the use of Pepcid in dogs online here: http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid
If you can, please keep a close eye on his 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 emergency 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 emergency Vet.
Respiratory Rate - if he is continuously panting throughout the night, this is a sign of shock and or pain and a signal for a trip to the emergency Vet.
Best of luck with Scout and do take him in to your local ER vet tonight if these symptoms continue. I hope all of the above makes sense? If you have more questions or if I can help in any other way, please do not hesitate to ask! If you would like to accept my answer, please press RATE OUR CONVERSATION (I am not compensated in any other way). Bonuses are always welcome. Thanks! I hope to work with you again soon!
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