As Yer_Man says, there's nothing to be done about the pictures you've unhidden, but for the future, here's what I do and what you can do after you round up and corral them again:
In Hidden, I Select All, (I check to sure to get them all,) and then I go to More (•••) and choose Add to Album. I Hit + to create a new album, and I name it My Hidden. It's weird, because when I look in this new album it's totally empty! They're all hidden, of course!
Then, when I want to look at the pictures, I can go to Hidden, select them all, and choose UnHide. They will disappear from Hidden, which will now be empty, and all my formerly hidden pictures will be visible in whatever albums they come from. But then I can see them in the My Hidden album! When I'm through, I can go to My Hidden and re-hide them all.
If I add more pictures to Hidden, I try to be sure to add them to My Hidden, as well, so I won't lose track of them if I ever unhide them.
Maybe that will prevent the next accident.