This video is unavailable because we were unable to load a message from our sponsors. If you are using ad-blocking software, please disable it and reload the page. Embed Code Restart Playing WATCH MORE VIDEOS FROM THIS EPISODE > When you're scared of the unknown, your biological warning system sounds off — your adrenaline kicks in and fear takes over. Is one of The Doctors willing to face his biggest fear and jump headlong into what he dreads the most? ShareTweet
