CRITICAL: FROTHING MOUTH AND SEIZURE IN MY DOG

My dog suddenly started having/experiencing a serious seizure. He's foaming at the mouth and can't stay still. I don't know what to do next. Please help! Is this a sign of something really bad? I'm so scared, he's my best friend. My Canine Companion is Experiencing a Convulsions, Frothing at the Mouth It's incredibly frightening to witness your