I agree with the drink coffee answer. Green tea also gives a natural energy boost.
At work, you really need to put on your best face forward, but on your personal time, it's a different story.
When you are away from work, try to do more recreational things than usual. This may involve watching comedies on YouTube, reading books, interacting at other forums with people who are going through similar turmoil, etc.
And don't beat yourself up if you sleep too much, or eat some extra comfort food. Just say "I'm going through this rough patch, I will try to make myself feel good so I can eventually recover from all of this"
Eventually, things will come back to normal, and it will be easier for you to focus at work without even trying. Let the healing take its course.
One more thing...
If these unpleasant emotions arise at work, try to find a place to be alone, and allow yourself to ruminate and go through these thoughts. Lot of people suggest "not thinking about it" and "occupying yourself", but these thoughts will keep surfacing again. Allow yourself to think about it, and remind yourself these are just thoughts (we are all human, we get thoughts, it's just like breathing).
If you allow yourself to think these thoughts, even for 5 minutes at work, the wave passes and you can continue being productive. And if the thoughts come up again, allow yourself to think them. Eventually they decrease in frequency till they disappear.
I suggest reading "Mindfulness in Plain English" (about 70-odd pages, will help you see things through different perspective). And https://buddhism.stackexchange.com/ may have some universal ideas for you.