I had it happen to me Christmas time i worked the dog on the Saturday and on the Tuesday I noticed he looked like he was pissed falling about in the kennel then he fell over he went all stiff, then he come around after a few minutes this went on for a week or so he would be fine soon as he walked the length of the garden he would just fall over again he could feel it coming on in the end as he put himself in position ready for it, I couldn't see him like it anymore so I put him down I don't belive it would be fair to try and work a dog that's not physically and mentally fit.