If she's sleeping her halo would be disappear. If she's still awake a little her halo would fade a little and go back to it's original brightness.

NobleJack said:

If she's sleeping her halo would be disappear. If she's still awake a little her halo would fade a little and go back to it's original brightness.

Which means she's conscious and is just enjoying the moment.

As a side note, the halo is a useful feature so that students can easily identify downed targets, preventing unnecessary bloodshed.