Easier To Be Cogent

I'm a pretty goofy, random person.  Talk with me during the day and you'll see me cracking jokes and saying silly stuff out of nowhere.  It's a good time.  You'll never know what I'm going to say (and honestly, neither do I), and there is always something to say because of it.

But when you catch me at night, things are much different.  In fact, they're nearly opposite.  I don't have much to say.  I don't start conversations, and nothing is random. I think it's because I'm so tired by night.  I can't be random because it takes way too much energy to create something from completely nothing.  I only have the energy to make thoughts that immediately follow previous thoughts (which is what normal conversation is).  When I get even more tired, I lose the ability to even start conversations; I can only respond to them.

It's a strange realization that it's easier to be cogent.  A logical conversation takes way less energy to hold.

But it's not entirely fair to say that its easier to be cogent.  It simply takes less energy.  If I am brimming with energy, it will be easier to be random.  I will want to burn all that energy as much as I can and do it by coming up with randomness.  If I am that overloaded with energy, I can hold a cogent conversation, but it will be a serious chore because I will want to do anything but stay on topic.

I'm not sure if it is like this for other people.  I feel like it's the opposite.  Traditionally, people who are well-rested will easily have straightforward conversations and the sleep-deprived will be loopy and goofy.

How does it work for you?  How does the time of day or the level of energy you have affect your mood or your writing?  How can you make that work for you?