Trauma is a pretty broad topic to give advice on, just because there’s such a range of reactions to trauma. There are wrong ways to do it, unfortunately, but there is no singular right way. There’s a lot of freedom with how to approach it!
First rule: TAKE/WRITE THE TRAUMA SERIOUSLY. If you are traumatizing a character, whether for the sake of the plot or their arc, commit to it. Make sure readers know this is a horrific experience. The plot and cast have to take it seriously before the readers can.
For reactions, the five stages of grief are kind of a good starting point. (Denial, anger, bargaining, sorrow, acceptance.) (Also notice I said starting point.) They get overhyped when it comes to talking about survivor reactions and how popular culture views this, but really, they are common reactions.
But keep in mind that you can go through them in any order! You don’t have to use all five, either. They aren’t a five-part process then you’re done; they are five things you will probably go through when dealing with grief.
A lot of trauma reactions can be sorted into those categories, at least on a base level. Of course, individual behaviors and reactions vary, but they’re still really good starting categories. Avoidance tactics can be denial, self-harm could be bargaining or sorrow or anger, and so on.
Don’t be afraid to think of it in the context of “what the plot needs” or “what the character arc needs”, though. You are a writer first and foremost, after all. A lot of hero stories have a traumatic backstory in order for the hero to grow (or even start their journey). This is fiction, and you’re creating it, so as always, make plot points serve you best.
Talk to survivors, whether a similar situation or even different ones. Find out what is real and contrast it with fiction you know, well done or not. Figure out what works in a story. Figure out what will work for your story.
PLEASE keep in mind what your character is already like! Keep in mind their existing characterization.
Then take that existing characterization, and twist it. Trauma can and will change a character’s behaviors/motivations/mindset, so it’s 100% okay to make jarring changes to them. Part of why it works to unnerve readers it because it’s so jarring.
(Just don’t take it too far. It’s a thin line and it’s a difficult tightrope walk, but it can be done.)
The peppy character suddenly losing their pep and being quiet and depressed is a common fiction reaction to trauma (Sayori from Doki Doki Literature Club, Madoka from Puella Magi Madoka Magica, any sad episode of Spongebob). Angry outbursts from happy characters are also common (like anything Naruto says ever). Or really sorrow-filled outbursts from angry or stoic characters (Homura from Puella Magi Madoka Magica, Bakugou from My Hero Academia, any time Dean actually showed emotion in Supernatural).
A shift in personality is a really great way to set the new, terrible mood, let readers realize how bad it is for your character, and let the incongruence drive in how bad this fucked up your character.
That said, you gotta keep some core character traits. Even if your character does drastically change, let them keep some, even if it’s little unimportant but recognizable behaviors. Let them remain identifiable as That Character for your readers.
Also, very important to note when writing grief or trauma—your character’s “main” reaction doesn’t have to happen right away.
It shouldn’t be “over” after a short bit, but some people do recover faster than others. Sometimes, it can get dragged out. Other times, whether due to that character or the overall plot, it doesn’t.
Trauma isn’t easily fixed, but in a lot of adventure/action stories, you’ll see cases of where it’s pushed aside for fights/battles/wars/for the greater good. This works, and can work very well, but keep in mind that it usually just creates an even bigger breakdown later. You can’t push it off forever. (And that later breakdown can be very narratively satisfying, says the sadist writer.)
Fear is a big part of trauma, too! A lot of writers seem to be afraid of making big macho male characters experience fear, or shy away from the nastier or less appealing sides of fear. It’s alright if you don’t want to use everything, but be aware of it, and don’t be afraid to make your character afraid. A lot can change a character, but few things can change a character as much as fear.
For denial, common tactics include avoidance, either literal cases of avoiding certain places/things/people, or in the case of avoidant behaviors, drinking, sleeping around, drugs, even things like reading or playing video games too much. It is tied into doing something else so their brain doesn’t have time to think about it. Workaholics can also fall into this.
There’s no wrong reaction to have to trauma, and chances are, there’s some way to swing almost any kind of reaction. Maybe your character bursts out laughing at their best friend’s funeral. Maybe your character decides to do increasingly dangerous adrenaline rushes because it’s the only way they feel “alive” anymore. Maybe your character can’t stand a specific color or smell, or they develop a new habit to do precisely at 5pm or else, or suddenly they’re making too much or too little eye contact. So much is malleable and usable.
However, make it recurring (if it makes sense for your character’s arc/plotline). PTSD is a very common recurring-type reaction to a traumatic event—it’s in the name, after all. Whether this means flashbacks, or nightmares, or any kind of trigger. Trauma reactions don’t vanish and aren’t just once.
But it also doesn’t have to be as serious as that. Maybe it’s just a habit that they picked up to cope and it stuck around. Maybe they don’t drink at all anymore, even though they used to be a party animal. Maybe they go to church now. Maybe they use public transportation instead of driving. Let the little things tell as much of a story as the big things.
Trauma is serious, and it changes a character. Let it change them, and commit to it. Try not to let your character bounce back immediately or fully. Let them struggle with it, in big and small ways, and let your readers see and experience their struggle. It’ll create a more realistic, more respectful approach.
