Anything over 5 grams is considered a "heroic dose" generally. I've done it myself when I was younger a couple times and had a similar experience as you, but then I continued seeking that same experience and after a few more times it ended similarly to OPs story. Now I can't even do mushrooms in my house without intense paranoia.

An analogy Ive found to hold true is, If you think of your mind as a rubber band, you can continue stretching it out as much as you want, but it wont always form back to it's original shape after a while.

Shrooms will hit differently every time my guy. Even if it's the same strain from the same batch you grew yourself. There are so many environmental factors that also come into play while on psychedelics and the vibe can change from great to very, very dark in seconds. And to be honest, 3 grams is actually a fairly strong dose. I know you mentioned you've done 6gs before, but 1.7 -2 grams is more so "common" dose I guess you could say. Lots of people will start with only 1g or less.

I've also done heroic doses of shrooms and acid and been fine, but I've also lost my mind on just a couple grams more than once as well. Glad to hear that it seems like you guys at least learned something from it. Safe journeys to both of you!