I know someone from a chat service I am on. We are not close friends; in fact, we barely know each other.
We ended up in a brief private message. In a tangent related to what was being discussed in chat at the time, in which I was only vaguely participating, they began to dump medical history, anxieties, insecurities, concerns, ongoing struggles, major life events, and traumas to me. This came out of the blue, and was entirely unexpected. I didn't invite this, and it has now happened multiple times.
I am not emotionally equipped to support them. I'd want to - they definitely need some kind of support. But I would be grossly overextending myself in doing so, and I can't put time or energy into it. Additionally, many of these things are not actionable. There's nothing to do about it - it's just venting. But it's venting that gives them panic attacks, and which they're not dealing with in a healthy way.
On top of this, I'm already in support relationships with too many others. As a result, as unfortunate as it is, I have to draw a line: my private messages are not open for me to support them. I might still chime in if there's something specific and tangible I could help with, and I see it elsewhere. But otherwise... I can't do this job.
I need to send this signal to them in a plain and clear way. I want to do it in a way that doesn't hurt them - make them feel rejected, like they're a burden, or otherwise worsen their current state. If I felt that simply not responding would do that, I'd go for it. But I don't think it will. So I have to say something, but I have no idea what.
What can I do in this situation to signal that I'm not open to hearing and supporting this at this time, in a way that's reasonably sensitive to their currently fragile state?