From Michael Rosen's Sad Book

Sometimes sad is very big. It's everywhere. All over me.

Sometimes I'm sad and I don't know why.
It's just a cloud that comes along and covers me up.
It's just because.

Maybe it's because things now aren't like they were a few years ago. Like my family. It's not the same as it was a few years ago. So what happens is that there's a sad place inside me because things aren't the same.

And sometimes I write about sad.

Where is sad?
Sad is anywhere.
It comes along and finds you.

When is sad?
Sad is any time.
It comes along and finds you.

Who is sad?
Sad is anyone.
It comes along and finds you.

Sad is a place that is deep and dark
like the space under the bed

Sad is a place that is high and light
like the sky above my head

When it's deep and dark I don't dare go there

When it's high and light I want to be thin air.

This last bit means that I don't want to be here.
I just want to disappear.