What does "heaviness" mean in the lyrics below by Adele?
When will I see you again?
You left with no goodbye, not a single word was said
No final kiss to seal any sins
I had no idea of the state we were in.
I know I have a fickle heart and a bitterness
And a wandering eye, and a heaviness in my head
But don't you remember, don't you remember?
The reason you loved me before,
Baby please remember me once more.

Question

What does "heaviness" mean in the lyrics below by Adele?
When will I see you again?
You left with no goodbye, not a single word was said
No final kiss to seal any sins
I had no idea of the state we were in.
I know I have a fickle heart and a bitterness
And a wandering eye, and a heaviness in my head
But don't you remember, don't you remember?
The reason you loved me before, 
Baby please remember me once more.

Answer

and the implication is they are sad thoughts, weighing her down (a heavy heart is a worried or sad heart)

Answer

It is a metaphor referring to thoughts. She says her head is heavy because there are so many thoughts inside it.