Though I try to hide it - it's clear,
I wear goggles when you are not here.

The story:

It was last week at Odeon of all places. They were playing it over the tannoy and I hadn't heard it in ages. And I was just singing along and it hit me like a rock in the face.

I used to think she was in a swimming pool and trying to catch up with her fish who was swimming away and 'choking' by saying GOODBYE (previous lyric)

Hence the goggles thing.