a lamp to my feet

Oh, how much a perspective can change
In only just one week.
Life can seem hopeless one moment,
And the next moment so sweet.

But then I find I'm back again,
Fluctuating so easily.
Back where I started, like I never parted
With the fear that's haunting me.

When everything is changing
How do I know what to believe?
My emotions are unreliable,
But Thy Word is a lamp to my feet.