Do not read if you feel so.
Apologise profusely, say you are not in the right mindset to give a good reading, and re-direct your seekers elsewhere.
That's what I do (I'm no stranger to depression). Disappointing all round - but better than forcing out a reading which may quite likely be coloured by how you feel.
I'm so sorry you are feeling low. I hope that it passes soon.
In my case when I arrive at such a point, I know I just patiently have to wait to work through it. And otherwise - I keep up with doing the things that I know help to keep me upbeat and have a more balanced view on things.