Oh god.. i'm installing the game right now.. and after reading that i'm not sure if i'll ever play it. I'm also arachnophobic.. it's terrible to find games you can play, now where the animations and designs look more and more realistic. I played reconning with fear, skyrim with the "nospider bearspider" mod, nearly every other game with spiders i deccided not to play.. maybe someday the witcher with some kind of mod.
But to explain how that trauma feels if an arachnophobic see a spider you could imagine that you see suddenly a real picture, of your murderd parents, child, sister or friend. Imagine that. You do something, suddenly there is that, out of the nowhere if you didn't prepare yourself on seeing that.. thats the same feeling with jumpscare spiders on an arachnophobic. Not just in games but also in real life, seeing a spider to close to yourself. If its far away or tiny, you can prepare yourself going on a closer distance, but if you detect it suddenly, there is the trauma. And there is like with the picture no difference within "on a screen" or in real life. But the discusting thing about, in games the spiders are more terrifying designed. They are crule disgusting big monsters which are actually attacking you! I don't want to bring closer details to my comparison with the picture, but maybe you get an idea how that fear feels, if your are facing them.
My reaction is often that i feel warm and cold, i'm shaking like hell, my ears becomes deaf, hear nothing than a swoosh, sometimes i can't even see anymore, everything turns black and my heart is racing. Sometimes minutes, sometimes 1-2 hours.. not everything, that i cant see holds up to about 5-10 minutes, that i can hear up to about 30 minutes, but the other things can stay quite long. Maybe you can make another comparison to a harder car crash.
I personally search sometimes for hours to find out if there are spider or spiderlike cratures in the game. And try to watch some youtube videos to get an idea how it will be to meet them ingame. The video isn't that terrifying if you dont watch if full screen. The spider is more tiny, you can look away knowing someone else is dealing with it, who dont fear them. But didn't be prepared makes it a hell. You don't want to die, you don't want to leave your character alone and let him die on the spiders, so i personally find myself often first running away or make a few attacks, but will have that panic attack.. better idea would it be to just look away, turn the sounds down and wait until its over, but at least i can't think in that moment and make often wrong decisions which make it even worse.
sorry for that long comment, but i try to give you an idea how it is to have a phobia. My biggest repect to everyone who can face it. I can't, at least i can't without preparing myself.
And if someone from EA reads this, even if you don't do something in the fallen order, please consider that in the next games, addons or whatever. arachnophobia is a quite popular phobia, maybe there is a solution with some other kind of creature and we are able to play that without spoilering us and we dont have to deal with the panic attacks of the phobia, snakes are also a very common phobia, but i personally dont have a problem with them.
Funny thing tho, i don't have that big problem with scorpions. i don't like em, but they didn't trigger some sort of panic, at least for me. If this is common to aranophobic people, maybe they are an alternative solution to spiders in games.
There's lots in there that's helpful for navigating around the spiders like calling out the spawning areas and sharing how to minimise/avoid those encounters. Really great post. 
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I'm so honored if it helps minimize fear for people and enjoy this fantastic game. 
