We have a 4 month old lab puppy who is normally a total boisterous lab. She suddenly seemed to sit down earlier and whimpered a little and it seemed her heart was beating fast. She wouldn't move - even for food. We examined her as best we could but couldn't find anything obvious. It seems to be her back right leg causing the problem. She did finally eat but won;t come for any treats. She went into garden for a poo and then hid in bushes. DH got her out and we got her into her basket and she slept for a while. She is now up and awake but obv not happy. Very sad and obv in pain. We have no idea what has caused this. Any ideas? Any suggestions?