One of the side effects is aggression. here i'll try this, anecdotally my neighbor was prescribed 5mg (20mg is max dose) for short term memory issues, and he said "it's a good thing i wasn't prescribed more, i would have killed my wife." This was so out of character for him, i've never heard him raise his voice or say anything in anger in the 10 years i've known him. He and his wife are a normal happily married (like 4 decades!) couple of awesome people.
So, yeah. I'm starting to notice a bit of a double standard on this site with more things than "google bad."
In regard to tinnitus, just a few weeks (3) could be plenty.
Amantadine could be a bit safer for longer-term use, but it too carries behavioral risks.
Verbal dominance (or slight verbal aggression) is actually not a side effect per se; it's IMO a primary effect, although its observance depends on the baseline state. It's a genuine state of power, of not putting up with bs. Unfortunately, however, this power will last only as long as the memantine intake lasts. The names adamantane diamondoid mean something. As for physical aggression, that should be quite rare indeed.
Calling it a side effect is like saying that feeling energetic is a side effect of caffeine. If you're already very tired, then you won't even have this effect anymore from caffeine until you're back to a baseline state.