It seems you have had unusual experiences. This is not the norm when separating cats during introductions.Originally Posted by feral65
I do not recommend shutting your cat in a room for the sole reason that your existing cats have already claimed that space as their own. While it may seem to you the cats are "less intense" after a few hours, things can change very quickly once you let the new cat go. the existing cats will likely immediately go for the bathroom and possibly even "mark" it by peeing. they will then seek the new cat, who likely ran for the nearest bed to hide under, where he/she will stay for days.
Trixie, you handled the introduction very well. As most of us here at TCS will agree, it is best to do gradual introductions. When Mika came into our life she was easily 1/2 the size of Bijou and for us to leave them together unsupervised would have been more cruel on our part IMO. We did a very slow introduction (4 weeks) with supervised time together before ever leaving them together alone.