I'm not sure what's up with my 2 yr old Maddie. About a year ago she had this weird incident. She was running then all of a sudden she jumped up in the air with all fours then she fell down stiff and landed on her side. She just laid there. I ran up to her and tried to calm her. She looked scared so I just petted her until she seemed to recover a bit. I thought maybe something scared her and freaked her out. Yesterday the same thing happened but I was close enough to see exactly what was happening. We were walking up a hill and she was coughing. She began to wobble and it was so strange all four legs spread out. I thought she was going to injure her back. Then she fell to her side and laid there. I kept her calm until she was able to get up. Last night she tried to jump on my bed and I heard her flop to the ground. I got up and she was laying on her side with the same look on her face. She seems ok today though not as active as normal. Her gums seem a bit pale to me but not white or gray. She has been to the vet many times for various reasons and they have always said her heart sounds fine. I will take her to the vet but hoping this sounds more like vaso vagal syncope?
Sounds exactly like my little girl, who has Cardiomyopathy...
Boxers are prone to this and it wouldn't surprise me in the lest to have it diagnosed in your case...
My vet couldn't diagnose it from their simple testing and after three episodes and doing some blood work and listening to her heart they still could not diagnose it... I had to employee a cardiologist to do a Holter test on her which confirmed the issue (along with a ultrasound and physical exam first by the Cardiologist).
With the description you gave, it is EXACTLY the same issues I had... she would be "wobbly" on her legs and had a cough and would "pass out" stiff like she just died... This would happen during play and at times of rest... didn't seem to follow any rhyme or reason as to when it would occur.
Since getting her diagnosed and on meds... she no longer has any wobble or cough and hasn't had a passing out episode. Her latest Holter took her from 12,000 irregular hear beats in a 24 hour period to a total of 8 in 24 hours... 8 total irregular beats was more than I hoped for and is just amazing...
If I were you, I'd seek a Cardiologist and have a exam/holter performed. It may cost 500 dollars or a bit more for the initial exam and holter, but a cardiomyopathy could easily kill your pup if not treated. For me, I'd rather know for sure what I was going on than just hope it was not a heart issue.