The human mind seems to be a restless machine, leading us to whatever kind of states it wants.
Thoughts are running through our mind the whole day long, restlessly and normally, we are in no position to decide if they stop or go on.
The mind works within certain frequency ranges, depending on the daytime.
But no matter what the state of the mind is, there is an UNBALANCE between the activity of the left side of the brain and the activity of the right side.
This happens in any untrained mind and this causes even psychical diseases, if the imbalance grows very high.
But normally, the result of this imbalance is only the impossibillity to control the activity of our brain - our thoughts - and controlling the thoughts would be a great help in any psychical activity.
Please read further on  http://www.graviflight.de/Mind/mind.html