One trick I use when I flit from one activity to another especially when there is a deadline is I write whatever that comes in my mind in whatever order they come out.

Once something is written my stress level goes down and I can then edit it just fine.

My suggestion would be to lay down and close your eyes for like 30 minutes. Set a timer so you don't lose track of time. You don't need to sleep but you need to give your brain a break. Next get some caffeine and food, preferably something with significant protein. The caffeine will help you focus. It's ok that you can't do it right this minute. Think of the laying down and eating as your setup. Once your body feels a little better and has some food to digest the stress will subside a bit. Not eating enough tends to make it worse so just getting food in your face will help a lot. They call caffeine the poor persons adderall for a reason, it does help. It may make you more tired if you don't have enough though so just be aware of that.