Vocalist and guitarist Mike Halls said:

I want to write about things in my life, what we’re feeling, whether they be sad or joyous. Emily is about someone very close to us who was suffering from a severe bout of depression. It’s us reaching out and saying, “we know you’re ‘unwell’ here and not just ‘sad’.” The ultimate thing is to take the deepest emotions and work it in to a message that isn’t miserable.
Source