>small amounts
alien thoughts, moments of epiphany, minor auditory distortions (echoing among other things) slight visual distortions (breathing surfaces, flowing of patterns, color vibrancy, light saturation), prone to laughter
>medium amounts
difficulty controlling thoughts (you begin to be increasingly influenced by your environment), you can't tell if you thought something or said it out loud, increasing open eye visuals (heavy flowing and breathing, color distortion, shape deformation), increasing auditory effects, pronounced closed eye visuals
>large amounts
it becomes difficult to interact with your environment and perform mundane tasks, illiteracy (even letters you would normally recognize appear to be alien hieroglyphs), difficulty communicating meaningfully, intense open and closed eye visuals (sometimes so intense you can't tell if your eyes are open or closed), ego death (you forget you are yourself, sometimes you even forget you're a human being and forget that you're a person who took a psychedelic), trance like state, breakthrough experiences, time becomes meaningless, powerful body sensations

This is just a general guide that mostly applies to shrooms and LSD, if you take something like a salvia extract or DMT you will likely jump into an entirely different reality for a brief time. If you take a deliriant you will experience many of the above but with no ability to distinguish it from reality, which can be extremely dangerous if you aren't in a controlled environment