Sometimes I sleep

Sometimes I sleep.
why, not to rest, but because I must.
if I didn't sleep I would relax.
but that is not allowed.
Sometimes I sleep.
and sometimes you listen to what I have to say.
and sometimes you forget me.
but mostly I wake.
Sometimes I sleep.
when you have criticized me for the last time.
when I am tired of listening to you whine.
when the day is over and the next has begun.
when I am so tired
I have become wired.
Sometimes I sleep.
But not very often.