Ear worm
Voldemort new this was down to Harry the only problem, was he wasn't asleep. It was that blasted song it was playing in his head, and the worst bit was he now new all the words. He'd have to stop himself singing often he'd see the words of the song emblassened across his vision.
A cheerful message of hope, he'd done a spell to find out what the song was, which some how made it worse. It was a Muggle song, and he couldn't get it out of his head, no it wasn't constant but sometimes he'd find himself humming it.
Was he coming undone? If he was then this was torture. He taken to singing in parseltongue so at least none of the other death eaters would understand it. Nagini on the other hand seemed to know the tune as soon as he started, although she had grown up in the Muggle world before taking up residence in the freak show. That was before when she was still a woman with a blood curse, now she was just a snake.
He hadn't realise that Harry was so sadistic. It had been 3 months so far, 3 months of love shine a light by Katrina And The Waves.
Harry wasn't just affecting his dreams anymore.