By now you’ve seen the image floating around social media about what to do if a Service Animal wearing its vest approaches you without its human. Some service animals are trained to go find someone if their human has a medical emergency.
So yes, knowing this is important. But please, if a Service Animal comes to you while you’re at a convention (or anywhere, really), before you follow the animal anywhere, make sure you ask another human to find UsagiMed, a Public Safety person with a radio, or even call 911 if necessary. This will allow the person needing assistance to get the right medical attention as quickly as possible.
There’s nothing wrong with being over-prepared if someone is having an emergency. Even if it turns out to be something minor, you will have done the right thing by requesting help.
But this only applies if the service animal approaches you and its human is not around. If the animal is working, and its human is present, it’s usually best to leave them alone. If you’re interested in learning more about how to interact with service animals, here’s an excellent writeup on the do’s and don’ts for behavior around a service dog team (team = a dog plus its human).