I had to take Cleo to the vet yesterday. We came outside in the morning and she was drooling all over the place and teeth were chattering etc. I thought maybe either snake/spider bite having seen the same symptoms in Sheeba quite a few years ago; or possibly she'd been playing with a cane toad.
Anyway, took her to the vet, he thought cane toad and put her in the hydrobath to clean out her mouth and fill her stomach - the intention is to make them vomit and get the poison out - but while we were doing this, he noticed a bone wedged between her very back teeth. Uh-oh! So out came the pliers, and out came the bone! Result. A happy dog.
She had a temp though, and the vet said sometimes the stress of something like that can cause a temp, so maybe the same thing with Carrot.
Also, our old dog Sheeba had a 'galloped heartbeat' which was very similar to what you've described in Carrot, and she lived to the ripe old age of 13, which is pretty old for a big dog. Actually, she was classed as a giant breed because of the dane in her, so even more impressive.
So, after that long winded story, I just wanted to say, "it's probably nothing."