Light verse

I think in couplets when I'm tired
But when I'm woozy it gets worse
My sense of meter becomes mired
In less substantial kinds of verse
Until I force it to behave
And still pound out my thoughts in eights
Lest I begin to rant or rave
While every other line deflates.
For in my reeling state I find
That eight and six feels very right
So even meter is a grind
Whenever I'm up late at night.
But in the morning let me wake
In pentameter for God's sake.