Metaphors are risky. I thought the CERN fish video made (a primitive sort of) sense, but it's not going to work for everybody. And it only seemed to make sense to me because it fit a pre-existing notion:

Seems to me that physicists tossed out a useful working concept a century ago when they declared the "aether" to be imaginary. Literally, sure, there's no "fluid" filling up the universe like an ocean...but look at all the fields that we're told "permeate" the universe, and we're basically talking aether. Or The Force...

I watched the CERN explanation interpreting the Higgs field as a kind of "aether", and from that perspective, a field acting like a fluid, I could then imagine the different resistance of different fish cross-sections trying to move through it, and thinking that the force required to push against the "Higgs aether" is what translates into mass.

I'm not really sure I understand the Higgs field and boson, but that's my interpretion of the same video you saw.

How do you "add a huge mass, still unseen, to the Universe without going nuts"? Well, how about you call it "dark matter" and prepare a grant proposal to study it?