How true. Last night I was running from a tornado in my dream...woke up with racing heart.....then I LAUGHED!!! It took a loooong while to calm down, too. I thought, well, at least I got my exercise for the day.
Emotional stress, even if caused by dreams, can cause one's hear to speed up (race). Your body doesn't know your mind is dreaming rather than viewing facts. So you body gets ready to fight or flight (run).