How to stop rigidbody.sleep()

Lets say i have an object mid-air and is sleeping [[“rigidbody.sleep()”]]
how could i make it awake again and move to where it needed to move to its physics (Lets say it needs to move downward, because its up in the air)

Is there a function i am missing?

You can set Rigidbody.sleepThreshold to 0 to disable rigidbody sleeping feature.

    m_Rigidbody = GetComponent<Rigidbody>();
    m_Rigidbody.sleepThreshold = 0.0f;

rigidbody.WakeUp();
will force it to wake back up. more info can be found in the reference:
http://unity3d.com/support/documentation/ScriptReference/Rigidbody.WakeUp.html
this will reactivate physic calculations and if its using gravity it will fall to the ground