If you are getting stressed about things out side of your job and you are finding that it is impacting your abilities.... Talk to someone about it. Hopefully you are on good terms with your area supervisor or manage and they are already aware that you are getting a little more stressed then normal.
If they don't already know and they approach you about it, tell the truth. Thank them for noticing and explain what you have done to try and fix it. Ask them if they have suggestions. It is possible that there might be something that they changed that could be adding stress to you that you didn't know about it.
But above all keep calm. Understand that you are doing something wrong and that you are in need of help and explain this to them. This can be a hard topic to approach because you don't want to always be pointing out your flaws.
However, this might be take out of your hands if a coworker with their own and often loudly proclaimed stress problems might try to use you as a target if you are not careful. Don't say anything negative about them directly or in an aggressive manner. If you are the mature and understanding your managers could be impressed. (and hopefully turn their attention to the coworker.)
So remember, don't get stressed if you are left alone by the other coworker. Just ask your supervisor or manager for help until they come back because you can't handle everything alone.