In the first episode of the second season of Stranger Things, Will Byers (Noah Schnapp) starts having random "episodes" that briefly transport him to the Upside Down. His panicked mom, Joyce Byers (Winona Ryder), takes him to a psychiatrist named Dr. Owens, played by Paul Reiser — whose clinic is suspiciously located at Hawkins laboratory — to discuss what he saw and felt during the episodes. After the assessment, Dr. Owens tells Joyce that Will is likely experiencing something called the "anniversary effect," because it's been about a year since he first went missing.
"We see this with soldiers," Dr. Owens says. "The anniversary of the event brings back traumatic memories, sort of opens up the neurological floodgates, so to speak." Joyce asks what they should do when Will goes through this, and Dr. Owens says, they should treat him normally. "It sounds counterintuitive. I know. But I assure you that is really the best thing you can do for him," he says. While there's plenty of reasons for Joyce to be wary of medical professionals in her world, especially those working where Dr. Owens does, there is some real-world truth to this diagnosis.
The anniversary effect, at least, is real: It is defined as an increase of distressing memories around the anniversary of a traumatic event, according to the National Center for PTSD. Indeed, it does affect many soldiers, and a 1999 study on veterans found that 38% of participants' worst month for PTSD also coincided with the month when their trauma occurred. It's also common for people who have lost a loved one to experience these emotions around the same time of year as the death occurred, according to the Mayo Clinic.
Around the anniversary, someone might feel triggered, and there's a spectrum of reactions ranging from feeling bummed out for a day or two to having "significant psychiatric or medical symptoms." The symptoms that come with anniversary reactions aren't all that different from those associated with PTSD, and can include intrusive thoughts that occurred at the time of the event; avoidance of the place or situation where the trauma happened; feelings of sadness, shame, and guilt; and nerves. For what it's worth, "being transported to the Upside Down" is not usually a hallmark symptom, but everyone's experience with PTSD is different, and much of it has to do with the individual's personality. Maybe, the Upside Down is just a metaphor for a dark depression, in which case this could be totally accurate.
Since everyone reacts differently to PTSD, it may not always be the best course of action to ignore being triggered by the anniversary of a traumatic event, the way Dr. Owens initially suggests (he's got his own motives, after all). For some, it can be helpful to make specific plans for the anniversary date to help commemorate it in a way that feels positive. For example, some find that visiting a memorial site, choosing to be with family and friends, or making a donation to a related cause can be helpful. Perhaps if Will's community in Hawkins had taken steps to acknowledge the anniversary and severity of his trauma, rather than bullying him as the "zombie boy," things might have gone differently for Will.
Interestingly, many people who don't seek treatment for their original trauma will feel ashamed that they're still suffering well after the incident occurred. When Will had his first episode, he chose to only tell his mom and his friend Mike (Finn Wolfhard), perhaps because he didn't want to scare anyone or feel like he was being singled out, which is something that comes up throughout the season. Often the fact that people didn't seek help can be a sign of an avoidance behavior that's associated with PTSD, which suggests that they may benefit from help if they do feel comfortable getting it.
Time can't heal everything, but stressful symptoms due to the anniversary reaction usually decrease in severity over time. Therapy, meditation, and even hypnosis can help people manage their emotions and triggers all year long, according to the American Psychological Association. Reaching out to your support systems, including friends and family, can also prevent people from isolating themselves, which is common in PTSD patients, according to the APA.
Without giving away too much of the rest of the Stranger Things season, it's safe to assume that if anything, Will has support from his family members and his squad of friends. With their help, he's got a good shot of getting through this anniversary and many more to come.