The Deserted Castle

For the summer holiday, my friend's family went to Ireland. They rented a castle not far from Dublin. It was at least 400 years old, and in complete disrepair. There was only one bedroom, so my friend had to sleep in the bedroom. It was pitch dark during the night, and my friend couldn't sleep. Suddenly, he heard a knock on the door. He froze. It wasn't his parents, because they never knock. Who could it be? There were five more knocks. My friend slowly got out of his bed, and crept over to to the door. He slowly opened it, only to see -

Dara Ó Briain.

My friend let out a blood-curdling scream, fell over, and passed out. Much later, he heard the beeps of a hospital beeping thing. He heard his dad say 'wake up son.' My friend woke up, looked at his dad, only to see -

That his dad was Dara Ó Briain.

My friend let out another blood-curdling scream and fainted. Much later, he was awoken by a doctor. He held a mirror out for my friend to see himself. Only he wasn't himself -