Mindfulness & Energy.
When energy is low, the practice is dull & sleepy. Attention needs to be directed towards effort/energy. Applying effort to arousing energy is essentially a mindful skill and mindfulness is duly developed through the practice of arousing energy with this skilful effort. It is, indeed, the recommended way to commence a session of formal seated practice.
Faith & concentration are an excellent way of going to sleep for the same reason: it is a further skilful means in the cultivation of mindfulness.
Investigation becomes a mindfulness practice when it becomes too intense & needs trimming: or is required to counter balance faith or confidence.