Emotional contagion is a thing. Emotional contagion via social media is, too, apparently.
You didn’t know it, but Facebook allowed an organization to study you. They manipulated your news feeds in order to do so, prioritizing a slew of positive or negative posts.
And what did they find?
When positive expressions were reduced, people produced fewer positive posts and more negative posts; when negative expressions were reduced, the opposite pattern occurred. These results indicate that emotions expressed by others on Facebook influence our own emotions, constituting experimental evidence for massive-scale contagion via social networks.
Of course, this is all to ensure a better experience for you, the user, Facebook says.