A new study has found that happiness is contagious. People who have happy friends are happier, and even the happiness of friends' friends influences our happiness.
There is an obvious evolutionary reason for emotions being contagious. I suppose it started with fear, which spreads quickly in small communities under threat, ensuring that everyone reacts appropriately. So it's good to know that the positive emotions can also be spread in this way.
The conclusion from this study is that you should choose your friends carefully and prefer the company of happy people. Conversely, be aware that your own emotions have an impact on others, so if you are capable of remaining happy while your friends are depressed, this could help them recover more quickly than if you caught their mood. Try to identify only with positive moods in your friends, while maintaining your own happiness even while they are down.