I’m NOT a vet, but it could be a problem with the “inner” ear.
The Inner ear can affect balance: He may be getting dizzy.
The sound of the cap gun may have set it off.
As you know dogs hearing is very sensitive.
That’s my unprofessional opinion.
Good luck.
Thank you all for the replies .
When he falls over , his hody becomes a bit rigid , and he looks almost dead . After a minute , he snaps out of it .
All the medical jargon in Japanese I don’t always understand , hence my lack of description . The jist was he has a bad ticker and there isn’t much the vet can do for him . I just can’t accept that , since he didn’t give him a thorough examination IMO .
I love this dog almost as much as my wife !