Live or frozen? Is this a solitary seahorse? How active is it compared to when it was feeding? are there any new marks or patches on the skin anywhere? White tail tip?
I would not panic or anything, just watch your horse closely and make note of any behavior changes.
Oh, and the most obvious question is: How do you know your horse is not feeding? do you remove all uneaten food from the tank?
From the first pic, if it was taken in the last 2 days, your horse looks quite healthy.
Fred