Pull your attention away from thoughts, worries, planning. Plant your feet on the ground or your body in a chair. FEEL the weight of your body pressing into the ground or supported by the chair. Keep your attention on the sensations of your body being grounded and supported. When the mind tries to head back to thoughts, smile inwardly and pull it back to the sensations of contact with the ground or chair. This gives the mind a mini-vacation from all that chatter that ends up causing more stress and signals the system to let go.
Fill your belly with air, like filling up a balloon. Hold for a couple of seconds and slowly exhale, pulling your belly toward the spine, as if there were a string attached pulling it back. Let all the air out and do this one more time. Feel the air entering your tummy; feel the stomach muscles expanding; and feel the air leaving. This will immediately signal the stress response to calm down.
See if you can get yourself to yawn…a nice, deep, wide yawn. This may happen naturally after the first two exercises. If not, try to force a yawn. This immediately encourages more down shifting from stress.