It all depends on how much you smoke really. When taking lower doses and not breaking through, I can usually remember that I smoked SOMETHING to make me like this, at least after a minute of thinking about it.
On higher breakthrough doses though, I am completely unaware that I have taken something. It is a little frightening to be that gone and not remember how you got there, but once you have done it a few times its not as bad. You still cant remember though.
As for the mushrooms or cid, if you are still able to remember you ingested something, you took a small dose. I have had experiences on mushrooms where I have had ego death, and just sat in a chair staring at my surroundings twisting and warping into unimaginable shapes, then melting away to show a whole new plane of existence/world. At that point I was not even able to leave my chair, but was able to traverse this new world in my mind. It was like my spirit had the ability to roam, while my body was frozen in place. At the same time, I was completely unaware that this was not reality.
So it all depends on the dosage. These ego shattering experiences can be the most enlightening and life changing experiences you will ever have, you just have to let go and know that nothing bad will happen.
Edit: Also, like Teo said, DO NOT EYEBALL! I made this mistake my first time smoking, and smoked around 60-70mg...Worst/best experience of my life if that makes sense. It was the most frightening thing ever but the most blissful trancedential experience at the same time.