Trust me, this drama will steal your heart. It's one of the best Korean dramas I have watched till now. It's been almost 6 years I have been into Korean and while you were sleeping is one of the bests in my Korean list. It will give you chills. It's a suspense, thriller and romance type of drama. I honestly watched it more than 3 times... Couldn't get enough of it. And even now if someone would want to watch it with me, I would be ready. On top of that, Lee Jong Suk is my favorite actor. I have watched all of his works. But that's my thing. The plot itself is amazing. Go for it. You will feel lucky to have watched something so worth it.