Pink Floyd - Coming Back to Life Lyrics Meaning

Funny nobody sees that like a left behind message before having commited suicide.

He is saying to one person he used to trust that he didnt get the support he would have been expected, and that led him to fall deeper into darkness.

Looking through a window to the falling rain "dark and slow", the time lasping, long days, helpless, hurt: all that feelings are describing a deep depression.
"lost in thought"
"lost in time"

The shining sun is the "idea", the "solution": the end of the tunnel, the irresistible escape, the light, calling him everyday more and more, like a planted seed: once depressed person starts thinking about suicide, the idea grows slowly and only people interefering can stop the plant to grow, the final change to come.

The silences he refers to are the absence of this person, the un-answered calls, the support he did not get. This slowly became an obsession "I took an heavenly ride through our slience".
Again, lost in though, over-interpretation those silences, thinking in loop.

And then, he knows, he knew, that the time has come for KILLING the past and coming back to life. Starting again, on the other side.
The waiting had begun.
All this referes to the next and last step to change this life to go... well, coming back to life in a hope to be born again in a better life.

Depression is an heavy thing and some people want just to start again, start from scratch, anything but escaping their own pain and useless life.

Quite dark song for me.