Full body (and mind) engagement.
Have you tried the warrior pose in yoga? You can’t do it unless you have a full body engagement. The legs muscles are engaged, the shoulders, the neck, everything is engaged. And just like that, the mind is also engaged. Mind follows the body and body follows the mind.
The disengaged mind and disengaged body are designed, in my opinion, for sleep. There is nothing productive that can come out of a disengaged mind and body. The default, however, in the modern lifestyle, has become this only.
When you have an impending deadline, the mind becomes engaged. When someone is looking at you, the mind becomes engaged.
How do you engage your mind, when these factors are absent?