Okay, Lets talk about Mindfulness. The basics of mindfulness are that you live in the moment.
You don't worry about what has gone past, because it's happened and you can't change in.
You don't worry about the future, because whatever you are thinking about might or might not happen.
You live for the instant you are in, and unless you inflicting pain on yourself, right in this moment, there is nothing to worry about.
Therefore, you should be constantly calm and content.
However, it doesn't tell me what to do when I am REALLY tired.