Until yesterday, I thought the idea of FOMO was a joke. It stands for a "Fear of Missing Out" — the worry that, at any moment, a happening party is going on, and you're missing it. The history of the term has been lost in the internet archives, but it's believed to have emerged shortly after YOLO, in the days when two-syllable acronyms were the done thing.
FOMO, of course, came long before the internet era. Winston Churchill and Abraham Lincoln are two well-known FOMO sufferers. The latter was a notorious philistine who hated the theater, but went anyway.
It's now apparent that we need to start taking FOMO seriously. As with almost any word, it has been associated with a number of diagnostic illnesses, such as depression, anxiety, social phobias, and even psychosomatic illnesses. Can you imagine being so miserable about missing a party that it makes you ill?

The rest here.

Without any facts to back up the assertion, I'm not sure if it's true that Churchill and Lincoln suffered FOMO, but that's a new one to me. Also, that Lincoln was a philistine?! If only he'd told his wife, “Our American Cousin? Again? I hate that play. Also, Ford's theater is so far, the seats in the box are so cramped.”

I'm old enough that I really don't experience too much FOMO anymore, but Twitter does exacerbate a particular strain of FOMO that is especially destructive for writers, and that is a sort of intellectual conversational FOMO. The stream goes by so quickly, a conversation at the digital water cooler can pop up, happen, and then disappear back into the ether without you ever knowing about it. If you manage to catch up later, the moment has passed and it feels awkward to chime in and bring the blue lined conversation back into people's stream.

This type of FOMO isn't as gnawing as the sense I felt in college when I had nothing to do on a Friday night and the dorm was near empty, but it is distracting enough that trying to get out your 500 words a day as a writer can be challenging. There's always another browser tab waiting, a few more information nuggets dropped into the stream to skim.