You had recently transitioned from a human go a ghoul. It took a toll on your body and it made you exhausted, the growing of horns and the devil tail took everything out of you.

You got up in the middle of the night and went to the ministry's garden to get some air.

You heard someone walking around so you decided to go see what it was. When you went to check you saw a ghoul without his mask on and he was waving his hand in the water of the pond