Yeah! They are fleeting memories. These alter state of consciousness are so far removed from our day to day reality that they are difficult to bring back with us. I find that a lot of time the intense memory came back to me months later when I would do much lower dose.
I sometimes fall into deep trance for a couple seconds every now and then. This must be because those trip were so intense. It's cool to see people discussing about those substance here. I hope to see more.