to me comfortably numb is about drugs, but not completely. the first verse is the doctor talking to him and asking questions, and pink sings the chorus answering to the doctors final question "can you show me where it hurts?" every single line of the chorus describes perfectly how it is to be on drugs, but thats not the only reason he is why he is. all the bricks in his wall also put him into his mental state because he is "numb" to the outside world and all of reality. just as the line "a distant ships smoke on the horizon" means. its like being stranded on an island and seeing a distant ships smoke on the horizon which is your help to get home safetly but also knowing it is out of reach and you will never be on it. thats the same he feels towards reality. he knows reality is way out there on the horizon but also knows he will never be back in it.