The Japanese name of the drug is called LERITE , otherwise known as Enalapril maleate .
Also known as Vasotec, an ACE inhibitor, used in humans to treat hypertension, congestive heart failure, and cardiomyopathy.
I suspect your dog has a weak heart....excitement is causing his heart to beat fast...too fast to effectively pump blood in its weakened state. His blood pressure plummets, he becomes unconsious and shows seizure type activity caused by a sudden lack of bllod to hte brain. Once laying down, effective blood flow is restored to the brain and he waked up after a couple of minutes, initially a bit wobbly but then seemingly as normal as he gets.
No...not a vet...a paramedic :)
So sorry to hear about your buddy's troubles. Hopefully, it will be the kind of thing that can be managed for years to come.
I feel compelled to ask if the vet told you to come back for follow-up blood testing. We had a dog who went on this drug also when she was about 10 or 11 years old. The veterinary cardiologist was adamant that she had to have regular blood work to make sure that the drug was not damaging her kidneys. They demanded the same thing when they prescribed the drug for a friend's cat. It seems to be the standard of care in the U.S. with this medication. My impression is that it is a very effective drug for the heart but can be hard on the kidneys.
Our dog developed kidney failure a few years later. I'm told this is the most common cause of canine death so it could have been perfectly natural. However, our family vet felt that it was the price we paid for taking the stress off her heart with the drug.
There is a lot of info online about the drug. You might want to do some reading.
enalapril is an angiotensin converting enzyme inhibitor that is used for hypertension and congestive heart failure in people