I’m in a very similar boat. I, too, feel compelled to write about people, like myself, with mental illnesses that they continue to struggle with, and may not always succeed in overcoming. It’s something I feel pretty strongly about, in fact. But, obviously, we can only speak to our own truths, not everyone else’s, and honestly, that terrifies me—the thought that I might, without intending to, balloon outside my scope, fail to afford due consideration, and maybe even become part of the problem.
So, I can’t give you any truly definitive answers, because I haven’t necessarily found them, myself. But I can tell you where I am right now, and the thoughts and approaches I’ve picked up so far.
(I will note, for the record, that I have significantly more experience with, and knowledge about, mental illness than physical disability, so if my points seem skewed toward the former topic, it’s because that’s the one I feel more “qualified” (for lack of a better word) to talk about.)
On the topic of being a "daisy downer"
The first thing I’d say is that I don’t really think topics should be “off-limits” simply for the sake of escapism. I think it’s important, sometimes, to be confronted with a harsh reality in a story. Sometimes, a so-called “safe space” is, in fact, the best place to facilitate broadening one’s understanding of real problems. That’s my personal belief, at least. Others might disagree, and honestly, I think that’s okay. Desires for “true” escapism are valid, but not all games have to appeal to all audiences.
On the topic of representing issues responsibly
As for representing these realities responsibly, Eiwynn’s advice about seeking feedback from people with the struggles you’re trying to represent is a good starting point; doing research on your own will go a long way as well, of course. Having some sort of content warning is definitely a good idea, I think—making sure people know what they’re getting into will curtail a lot of negative reactions with regards to your “daisy downer” concern.
The other thing I’d add from own experience—as somebody who is currently in the midst of an attempt to tell a story with several difficult character arcs about mental illness—is that it’s really important to make a concerted effort to facilitate empathy. Invite your readers to see not just the end-results of your characters’ struggles, but also the very intense feelings and thought processes that accompany them, in a way that your audience can hopefully understand, to the extent that they’re able.
What this means varies depending on what issue, specifically, you’re discussing, of course, but there are a few avenues of translation that you can use to your advantage. For instance: not everybody necessarily knows what it’s like to be suicidal, but most people do know what it’s like to feel overwhelmed or helpless. It’s not the same thing, obviously, but it is an emotional foundation that you can build on, in attempting to foster understanding.
Some specific thoughts on mental illness / disability as it pertains to an MC
If it’s the MC you’re talking about, what this means is going out of your way to communicate specifically what the MC is feeling, and why—to the extent that the MC themself can understand it—they behave the way they do. The advantage of using the MC as a vessel for this is that you have free rein to describe their struggles in as much intricacy and detail as you feel is necessary.
As you mention, though, you do risk alienating people that want to avoid helplessness, and I think the important thing here is to remember that feeling helpless and being helpless are not the same thing. Most people, I feel, are specifically averse to the latter—the notion that the MC has no impact or driving force in the plot—more than the former. As long as you incorporate the MC’s struggles in a way that doesn’t invalidate their role in the story, I think the majority of people will accept, or even embrace, their limitations.
Some specific thoughts on mental illness / disability as it pertains to an NPC
If it’s an NPC in question, it’s a little more complicated, because the reader doesn’t get the privilege of seeing inside that character’s head. In this case, I think the most important thing is to present the character as a whole person not solely defined by their illness or disability—let the reader see the character as a person, first, and a representation of mental illness / disability more as an extension of that person.
With regard to stigmatizing mental illnesses, I think a lot of stigmas related to mental illnesses, at least in my experience, have to do with the perception that they’re somehow a threat to other people’s livelihoods—that people with “anger issues” will physically harm the people around them, that people with depression will emotionally drag everyone else down with them, and so on. With that in mind, I think another thing that’s important here is to show the audience how the character’s struggles can negatively impact their own life, not just others’—to show that the character themself is hurting, and, in many cases, in need of support. Again, facilitating empathy is key here.
And finally, some (less focused) thoughts on villains/antagonists with mental illness
You didn’t specifically ask about this, but it’s something that came up for me recently, so I’d like to talk about it, if that’s okay. I was recently involved in a difficult discussion about a villain in my WIP who happens to have a personality disorder (specifically, malignant narcissism), and while the conversation was settled amicably when I made it clear that there would be (and already are) more heroic/sympathetic portrayals of mentally ill characters in the story, it definitely got me thinking about whether I was, in fact, presenting this sort of topic responsibly. Is it unfair for me to portray this disorder—which I don’t personally have—in a negative light, even if I do so with as much consideration and authenticity as I’m capable of?
Honestly, even now, I don’t know if I really know the answer to that.
I guess the thing I would say about this—and again, I don’t know if this is the “right” approach, or if there even is one—is that despite the character’s villainous nature, I really want to approach him with the complexity he deserves, and—as with any NPC—display him as a whole person rather than a caricature. My hope is that people will still be able to empathize with him and understand his point of view, even if they can’t necessarily support or condone his actions.
And I’d like to believe that doing so will still be helpful in fostering understanding, or at the very least, avoiding stigmatizing mental illness more than it already is, but the honest truth is that I don’t know for sure. The mere fact that he’s a bad guy might be too damning. Like I said, this is an issue that I also wrestle with, and I definitely don’t think I have all the answers. But, that’s where I am right now, and what I’m currently trying to figure out.
Anyway, that’s probably a lot more words on the subject than you were really asking for, but, well, this topic is something I’ve been thinking on for a while, myself (and didn’t realize I needed to talk about until now, I suppose). Hopefully I said at least something that resonates with you or helps you in your process.
And if not, well, hopefully you at least found it to be an interesting read.