What Is Alive?

Ever feel like the world is a fantasy? Ah well, must just be me then....

What is Alive?

I sometimes think I've never lived,
it's all my imagination.
My mind is just some kind of sieve
and reality's its creation.

How can I prove this theory wrong?
How can I save my world?
I can't maintain this thought for long,
my mind will come unfurled.

All I know is that I think,
and apparently, therefore I am.
But then as quick as I can blink,
I'm right back in this jam.

Right so, I know that I am real,
but I can't say the same for you.
I can't tell if you can really feel,
Or are just a part of me, unglued.

If this was all an internal game,
and I was really clever,
when would I truly know its name?
The answer to that is never.

So which of these paths can I take?
How can I fix my brain?
I can realise, even if all was fake,
then you would feel the same!