It's ok to stress; only for a moment. But donot stay there. Whether you choose to be angry, upset, annoyed, take a nice deep breath, INHALE deeply, then EXHALE deeply. Take your time and slow down for the moment, feel you body at ease and be still. Know you are safe and about to feel better in a moment. Give yourself time to register exactly what you are feeling. For example, "I feel upset....my friend no-showed me at the library; I hope he is ok." Here is a tip, start with being upset at the situation, not the person. Never presume the negative and worst aspect of the possibility, but be aware of the possibility. Before we start creating our own story of why your friend no-showed you, we need to take a step back and realize there can be 100 different reasons, but only one is the true answer. We have no control over other people's behavior, mishaps, or their problems, but we do have control over how we behave when difficulties, problems or miscommunication arises. It is always best to have clear and open communication when you are making appointments or expectations. Practice inner peace, patience, kindness and non-judgment as a daily practice, so you are better equipped and can better manage yourself when inconveniences happen. So back to the friend who no showed you, best to calm your emotion, first, take 3 deep breaths, then communicate, express your honesty and authenticity that the situation upsetted you; then work towards resolving situation and build mutual respect and accommodation, trusting that this will not repeat itself.
Some simple suggestions to remedy stressful situations:
1) Identify the root cause of the stress; 2) Accept the 2 best natural ways to REMEDY/to minimize/prevent the root cause from happening again 3) Apply the remedy. If the mishap happen too often, you will have to re-examine if the relationship and situation is serving you and your mission in life.
Meanwhile, while in the process of examining the relationship, there are healthy natural approaches to rejuvenate and recover your body and mind in good timing: