Yes, it would be nice if we were always fresh, mentally alert, and feeling intellectually spry and creative. It would also be nice if I were young, had good skin, and could eat whatever I wish without consequence.
Yet, this is not the way life works, right? We are often tired, annoyed, anxious, burned out, ect. So, to wait for the perfect "state" would mean to wait in a perpetual state of non-productivity. So we have to train ourselves to write in different states, in order to become accustomed to it.
I also find that writing in different states and different moods can lead to different insights and perspectives. Also, you may find that you are able to engage in different aspects of the writing process more successfully in some states verses others.
So, try to make yourself writing when you are a bit annoyed, angry, hungry or tired. Even if it is for only five minutes, sneaking in a few minutes here and there not only leads to increased productivity, but can lead to an increased sense of self-efficacy as well.
This coming week, try to consciously written in states, spaces or mood in which you normally would not write.