Wow, I've dealt with this before! Hope you are feeling less stressed, and the job search is going well!

Some things I have done:
as others suggested, take every break entitled to - even if just walk outside it can refocus your vision from the job to things around you

Go to the restroom, wash your face or just run water over your wrists I found soothing

If you are able to use earphones or even just one earbud, listen to audio book, language lessons - something that projects to your life outside of work or goals beyond this office

flashcards on your phone - I scroll through cards on which I've written supportive things people have said to me, reminders of my goals, images that make me happy - basically reminders of who I am, who/what I love away from work

Take a break, call a friend just to hear a friendly, positive voice

what is called "forward thinking" in DBT: will this place, these people, have any impact or relevance to my life five years from now? Recall earlier situations where you felt this way, and how little you think of these people/places now.

Or what I call my "magic bullet" (eg guaranteed to work, right or wrong) and eat a candy bar or pastry and let the anesthetic of sugar and carbs lull me into sweet sweet numbness.... I also call this my "auxiliary" skill, and only use it when other skills haven't worked, too stressed out to deal. I don't gulp down baskets of muffins or a dozen donuts, one is plenty.

Take care