It is when you have so much to say, but then don't because either you are not sure about it or just feel lazy to think about its relevance
My colleague: Happy 2021! Hope you had a nice break.
Me: Same to you. Yes it was a nice quiet one. Hope you had a good one too
My colleague: Yeah I did. Was just glad to stay away from tech
Me: Hmm...
My colleague: I have been kind of annoyed with the lockdowns as it has limited my outdoor activities and made me circle back to tech for relaxation
Me: Hmm...
My colleague: Sorry for whining :)
Me: Hmm...
My colleague: Are you alright amigo?
Me: Yes, all good.
My colleague: No, just think you might be suffering from the 'Hmm...syndrome'
Me: Hmm...lolz...