Slowly and gradually when one start leaving all his identities, habits, attractions , desires then thoughts start reducing .When nothing in this world will create a desire to enjoy with our senses then, one enter thoughtless state.
This state help us to establish in the Self.
Thoughtless state can be maintained for one hour daily to any extent as one progress in its practice.
At the time of death as you are already well trained to achieve blank state, void state , equilibrium state and one has lost all attachments of this world then death will be powerless, it will not surprise you, you will not feel helpless, miserable. Infact you will remain in same thoughtless state even after death. This means Liberation.