When we feel stress, we strain inside without realizing it, it creates a blockage, the unpleasant emotion will thus be able to persist whithin us. Without realizing it, by fighting against, we feed it with our energy. If instead of fighting stress (anger, sadness, etc.), we accept it, the emotion will be able to free itself and begin to dissipate. Emotion is not us, it's only passing through.
Sit down, and close your eyes if you can. Take 3 breaths, INHALE DEEPLY, EXHALE SLOWLY, being careful of the beginning of the inspiration, until the end of the exhalation. Try to locate physically the stress, where is it in your body? Do not try, after these 3 breaths to be necessarily calmer, or relaxed. Stay attentive to each of your inspirations and expirations.
When you inhale / I'm stressed (say mentally)
When you exhale / It's OK to be stressed (say mentally)
Repeat this sentence at least 5 times, observe if there is a slight relief that occurs. Repeat as many times as necessary, and as often you feel like during the day.
You can use this simple practice every time you feel overwhelmed.