Give him space. When he feels the attack going on, he needs to close his eyes, forget everything happened around him, and just take deep breaths. Don't touch him, don't try to talk to him, dont do anything. That will make it worse.
Deep breathing, slowly inhale threw your nose out thee your mouth....try to focus on something pleasant , get your head away from what started the attack. Most important get his to seek professional help. There is good treatment, everyone needs a little help now and again. Good luck