Arjuna's grief finds words. He turns to Krishna and says: "Seeing my own people gathered here, eager for war, my limbs are giving way and my mouth has gone dry." This is the first sentence of his famous lament.
Pay attention to the shift in language. Moments ago, these same people were "supporters of wicked Duryodhana." Now Arjuna calls them "svajana" — my own people. The enemy has become family. The target has become a loved one. That single change in perspective is enough to break the greatest warrior alive.
The physical symptoms Arjuna describes — limbs going weak, mouth drying up — are exactly what happens to a person under extreme emotional shock. When grief or dread hits hard enough, the body responds before the mind can make sense of it.