Could be nothing but stress... It's a long season, the yanks series, losing road trip, and maybe he's taken their fall to heart, so to speak. I once thought I had a heart attack, but turns out it was just stress and heartburn. You get so panicky you're having a heart attack, you're heart starts jumping, beating irregularly. the stress of thinking you're having a heart attack snowballs and you think you're going to die and the heart gets more jumpy... It didn't help matters that a lady in the emergency room bed next to me coded (i.e. died from a heart attack) while I was waiting to hear back from the doc.
As soon as the Doc told me I wasn't having one and it was basically heartburn combined with stress, I immediately started feeling fine. Nothing in the world makes you feel better than to be told you'll live when you're not sure that's the case.... That night convinced me to take better care of myself and I've lost 30 pounds since then. Long term health wise, probably a good thing it happened.