When feeling overwhelmed and unable to focus, stop for a moment
If your mind is on "overload," that is your body's way of telling you that you need to stop and regroup for a moment. Take a few long, deep breaths. By doing this, you are slowing down your system, and attempting to tell your body to physically calm down. Close your eyes and do this for a few minutes, as you clear your mind temporarily of all thoughts.
Get moving, to help your body produce endorphins, or "feel good" chemicals
Another way to recharge your mind is to get up and do some sort of physical activity. Whether it's a brief walk, jog or ride on an exercise bicycle, do something to get your heart moving. Physical exercise will help your body to naturally produce chemicals called endorphins, that can help to improve your mood.
Be logical, not emotional
Instead of jumping to conclusions about the situation, be rational about it and calmly think of solutions to it. Be realistic in your assessment of the problem, and don't magnify or dramatize it in any way. Just take time to think it over without allowing emotions to take over. It takes practise to do this, but is well worth the work. You are re-training your mind to react more calmly instead of in the old, familiar ways such as panicking or becoming overly emotional. Write it down, and keep a diary of your progress.
Don't beat yourself up
Be kind to your mind. Let yourself make mistakes, because that's what learning is all about. Practise being understanding and supportive to yourself. Don't rely on others to do this for you, let it come from deep inside you, instead. If you grew up hearing negative things about yourself from those you love the most, you may be conditioned to think poorly of yourself. The only way out of it is through it. I know, because I've been there myself. The more I've practised countering self-criticisms with positive thoughts, the easier it got. I can slip into being hard on myself, but then I catch the problem and correct it. Remember, nobody is perfect, and mistakes are only human.
By battling stress and anxiety full-force, on a consistent basis, you can improve the quality of your life. Don't give up. Part of my success has come from being somewhat stubborn and tenacious about solving problems. I use all those fighting skills once needed for survival, now against the high emotion I no longer want or need. Most of my days are peaceful and calm. If a problem crops up, I deal with it. Before, panic would set in and I'd look to others to help me fix it. By believing in myself and my ability to overcome problems, my life has improved. If I can do it, so can you.