It depends to what extent you wish them to be unconscious, in my experiments with drosophila, to change the container, used Ethanol for them to get unconscious.
I was thinking of a situation more analogous to that of concussion in humans, for example after blast trauma. I am not an experimentalist, just curious as to the cause of concussion, which I do not think is due to brain damage.
A concussion is not mainly caused by brain damage by may also occur due to an injury with a mild to severe scale. Also, symptoms may vary according to extent of injury.