I saw that someone was confused about what it means, well obviously I don't know exactly but this is wot I think.
I think that it means if you have problems that you're finding it hard to forget, you need to find it in yourself to let it go.

"If you have to let it go
And these dreams keep you awake
If you have to let it go
Walk away"

I think it means that you shouldn't let whats happened in the past 'keep you awake' at night, you shouldn't let it take over your life, and even though it's hard you have to walk away, move on.

"And the waiting is the hardest thing to take
In an moment more before we break"

I think that means the waiting for the thing you've experienced to sink in, like for you to finally realise what's happen is really hard. And eventually you will break down, but then back to the chorus, you need to stop letting it control you're life once you've come to terms with it.