Tense is the opposite of relaxed. There may be a specific cause of the tension. More usually, several things may have come together to give this feeling of tension.
People who are tense tend to be snappy, irritable and quick-tempered. Code 10/7 indicates that this bad temper is due to underlying tension and not to what is happening at the moment.

At the same time code 10/7 is an appeal for relaxation: sport, humour, music, massage, etc.

Sometimes tension may be a reaction to something specific like a disagreeable meeting that has just taken place.