I imagine getting hit by Void damage (specifically a Nova Bomb) to be sort of like a concussion blast... As in, it's Gravity and Anti-Gravity simultaneously. You would feel a massive pressure, but at the same time feel like you were in a vacuum being pulled apart. Like every atom in your body was being expanded and contracted for a spilt second before you simply cease to exist. I don't believe you would feel much as it happens so rapidly. A void grenade would be the same if it killed you, but if it didn't, I imagine it would leave you feeling disoriented and weak, for a time.