Everyone has 'one of those days'. There may not necessarily be a reason for it, but sometimes just life, in general, can bring you down, and in these days it's important to put yourself first. Find something that allows you to escape the day and hit pause on life for a while or something that will cheer you up. Everyone is different, but let me suggest a few:
Read A Book

Watch A Film

Meditate

Exercise

Music

If you're reading this, I hope you do find your escape.
If you're having 'one of those days' remember everyday only has 24 hours in it, make tomorrow a good one!