Be it sadness, depression, or epidemic.
Emotions are a tool to be used to convey your feelings and that of your characters into words.
Use what you are feeling in your story; this helps your story feel deeper to the reader and can help ease your tension.
I use writing as a type of therapy. To help me through dark times, I write. By doing this, you will see a difference in your writing.
So, use how you are feeling, sad, happy, stressed. Put these into words and make your own world where you can visit during dark times.
I’m not saying that it’s easy. Because it’s not, it is hard but a necessary part of being an artist.