Spoilers for The God Complex, if you haven't seen it yet. My take on what the Doctor saw when he opened his door, 3 different versions in one. I personally feel that version #3 is probably the closest to being correct. Let me know which one you like best, or perhaps you have a different theory on who he saw?

Disclaimer: I don't own Doctor Who, yadda yadda...

He knew – he knew – that he had told them not to open their doors. So what excuse did he have to open his own?

It sat to his left, the 11 door marker taunting him from afar. What was he most scared of? Finding out would be beneficial, wouldn't it? Practical, even. After all, he knew what that creature was. He knew how to resist the praising. It wouldn't have any hold on him if he focused hard enough. He had no excuse not to open his door.

And so, he did.

The sound of the TARDIS's cloister bell was the first thing that hit him.

He knew that sound all too well. It was a frightening noise, but as he stepped forward to peer into the darkness of the hotel room, his breath caught and his twin hearts began to beat with ferocity.

"Of course... It would be you."

One

He stood at the window.

It was nothing like the Ganger situation. It was him. The Doctor. A perfect replica of himself, standing near the window. The Other Doctor, for they were even wearing the exact same clothing, turned from his inspection of the "window" and stared. The Other Doctor had his hands in his pockets, looking overly smug and confident.

The two stared each other down for a moment, the real Doctor knowing that this reflection despised him as much as he despised it.

He was, truly, afraid of himself. Not only for what he was, but what he was becoming. He had spent so many years in fear of the Valeyard, the evil version of himself that had tormented his sixth face. His greatest fear was that in trying to prevent it, he made it happen. Just like Pompeii.

He silently shut the door and suppressed a deep shudder of revulsion.

Two

Sat on the bed was none other than River Song herself.

She stared at him from beneath the helmet of a space suit, looking for all like a murderous creature, hellbent on ripping his throat out with her claws.

The suit was not the same as the one she wore to the Library, he realised. Amy had been the one to tell him of his death in 200 years. His own private fear, that River Song would be the one to kill him, hung heavily from his hearts.

He liked River. Perhaps it wasn't in the exact way that she wanted, but he did like her. He felt himself trusting her much more than he should, considering she had already killed him once. But then she had brought him back to life, sacrificing herself for him.

And he didn't want to die. He had been able to ignore it all before, for the sake of saving Amy and Rory. He had been terrified, but acting had always been a strong point of his. Staying strong for them was important.

River's glare unnerved him. He quietly took a step backward, shutting the door behind him.

Three

She was there.

Adelaide Brooke sat calmly on the end of the bed, seemingly resigned to her fate. To her right stood the Time Lord Victorious, his tenth face, holding her blaster to her head. His eyes were wild and triumphant, breath coming in heaving gasps as if he'd just run a marathon.

They both looked to the Doctor as soon as he cracked the door open. The look on Adelaide's face tore his heart to pieces. Accusing sadness. All his fault.

And then there was himself, in his brief moment of insanity. Sweat stood out on his neck and forehead, running down his face and disappearing into the folds of his coat. He stood at attention, ready to pull the trigger.

The Doctor was afraid of what he had been. The Time Lord Victorious had been an abomination. A vile, pus filled wound that Adelaide had healed all on her own. It was his fault that she was dead. And it was his fault that he had become such a scar on time. Disgusting. Broken.

He stepped back and closed the door, remembering briefly that he had had that nightmare hundreds of times before.