Pink Floyd definitely can't be related to ANY types of drugs in ANY way. for me it's a normal lyric about growing old.

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In the womb, the baby thinks that it's the universe. And when the baby is born, there is a glimmer of light.
I was there, but now I am here. So there are two things - me and the universe. The universe is there for me.
Then what happens? Other people. But the universe is there for you. Now tell me what happened in the glade.
I did something to myself. Like entertainment, like music, like a daydream. There was nothing there and I saw something.
I saw his head on the bonnet of the car. You can say what you like but I saw the bird of paradise spread its wings.
DO YOU PLAY BRIDGE?