Flow state

It's when you're fully focused on a task. People at competitive sports experience it a lot, but it can happen at many places in our life.

I had a professor that said that you were only really studying when the your house is on fire and you are not able to notice due to being so invested. He was describing flow (and also a very dangerous situation)

The concept of flow was developed by Mihaly Csikszentmihalyi as a part of his research.