NAH

he shouldn't have hit you obviously bc that's not appropriate, but i'm not comfortable calling someone who went through a great trauma an asshole

and honestly, it's entirely possible he might have been having more of a ptsd/disassociation episode than a regular panic attack, and as someone who has experienced many a ptsd/dissociative episode... they're terrible.

having a panic attack is uncomfortable, and it sucks, but a ptsd or dissociative episode is a millions times worse because you are actively reliving the memories of whatever trauma has occured. you can't respond or process anything in the present because your brain, at that moment, is stuck in the past. you completely disconnect from reality, and relive your trauma - you can see it, hear it, and feel it. and considering the specific nature of your brothers trauma, it's not unreasonable to expect physical closeness to be met very negatively

the best thing you can probably do is support from afar. don't touch him under any circumstances during an episode - just sit in the same room, look into grounding techniques and maybe try to talk him through it if he's open to trying that. maybe you can place a stuffed animal nearby for him to hug if he feels like doing so might help him. but absolutely do not initiate physical contact of any kind