No, I am not talking about a 1960s-esq, Hunter S. Thompson gonzo experiment. No Timothy Leary blotter paper or special mushrooms for you today (at least not due to my counsel).
What I am asking you to consider is the assumption that you must be totally "with it" and at your best and to write. I did not sleep very well last night, and woke up, as we say in our house, squishy. I don't feel very bright, and am not sure that I am going to write anything very insightful. Yet, I have some work on a chapter to do, and my calendar said that it was a writing hour. So, write I will (with this as a warm up).
Yet, I also know that I can take advantage of my different states, moods or spaces. Each allows for a different type of writing, and a different way of approaching a problem. While not a specific weakened challenge, I do suggest you learn to write under less than ideal psychic conditions. Spend some time writing when it seems less than ideal; you may learn something about your own process. You also may feel good about yourself and your fortitude and consistency by pushing through when you may otherwise not have.