I have just realised that I've somehow managed to disable comments from my blog. Please bear with me, I have no idea what I'm doing.
Two hours later..
Comments are back - I fixed it! I am so happy, I thought they'd be gone forever... I was trying to be clever by adding labels and tags to my sidebar and posts, but for some reason that automatically disabled my comments. I promise that I will no longer attempt to be smart and computer savvy when it comes to my blog.
Sorry for the confusion!