After you finish eating the mushrooms, you start walking again. But you didn't realize that it was not an ordinary mushroom.
After a few steps, you hear somethig in the woods. You stop to walk and look for what made the sound. However you couldn't find anything. Probably it was a wild animal. You shrug, and start to walk again. But you find that you can't move your legs.
If you look at your feet, you can see that they are firmly anchored to the floor. It seemed to have taken root in the ground. You panic, pull your foot, but still do not move. As you shift your gaze upwards, you can see that the trees have grown several dozen times larger, because you have shrank. Helplessly you stare what is happening. First, your legs get thicker, to merge and form a stem. Your skin becomes smoother and look like the mushrooms you ate. Over your head, your hairs get harder. Soon, it forms your big cap of mushroom. You surprised and try to remove it, but you found your arms start to shrink. Your fingers were already disappeared. Also your arms immediately decreased and sank into the body. Lastly, your face disappears and it makes your head is just a part of your stem. Your eyes and ears disappear. However somehow you can still see and hear.
So now you are a mushroom. But also, very magical mushroom. While you regret and despair, you hear the same sound again. It's also getting louder.