I can tell you from personal experience, the answer is no. Strangers do not stop. They do not ask if you are OK. It doesn't matter to them that you're crying, gasping for breath, quietly asking for someone to please help. To them, that's "crazy", and they're not going to touch "crazy" with a ten foot pole. They don't want to be associated with it. Or, to give them the benefit of the doubt, maybe they think, at least for us women, that we're just being dramatic, hormonal, emotional. That they have bigger problems than to help some woman that can't pull herself together and help herself (I can't speak from the man's point of view, as I've never been a man suffering from an anxiety attack or depressive episode in public). But I can tell you that I can count on one finger the number of times someone has stopped for me. And that person was in an elevator with me, so perhaps it was simply the proximity, or the fact that I was wearing a shirt that said "Out of Darkness Walk for Suicide Prevention" at the time that made her think that something more substantial was wrong. But let me tell you, that one person, she made me feel like I mattered when I thought I didn't. But that happens so seldom.
Let me tell you instead what happens: You have a panic attack, or anxiety attack, or (hypo)manic episode or are so depressed you can barely lift your head. Someone you don't know, or don't know well, sees or hears this. They get concerned, but not for you, for themselves. Because you're acting "weird" at best and "crazy" at worst. Maybe you're dangerous, they think. I better not let them near me, let alone help. Then, without speaking to you at all to find out what happened, to make sure you're OK they "take some action". Some cowardly, inappropriate action. Maybe they post something about it on social media "I just saw this crazy lady crying on the corner for no reason and begging for help. What a freak." Or maybe, if it's someone somehow associated with you - someone in your industry, or in your housing complex, they write something to you about your "behavior", or worse, write something to someone else and complain about you without any knowledge of what actually happened. Maybe you're then stigmatized and possibly discriminated against in the group or community, or whatever it is. Not overtly, of course - that's illegal. Nobody wants the ADA on their tail. But maybe you're glanced at sideways, or written off as less capable, or considered a "problem" that people talk about behind closed doors. All without anyone speaking to you to find out about your medical condition. And if it's someone you have no contact with - well, you just become that crazy lady that cries on the street randomly. Or you're nobody at all. Nobody deserving of help, of asking if they're OK. And that, to be honest, is worse. I've been an outsider my whole life. I get it. I've grown to accept it. But to be nobody, to be invisible? In avoiding asking if that person was OK, it might be the last thing that nobody said to that person. Because all they needed in that moment was someone to reach out and notice kindly, and nobody did. That person, in their eyes, is nobody.
So please before you judge, before you label, and before you pass someone by that looks to be in any kind of pain, stop and think - how would you feel if all you needed was someone to understand what you were going through, or at least to try to, and everyone refused, as if you and your pain didn't exist And maybe, next time, stop to ask. Or offer a tissue to someone crying. Or offer to listen to them. But treat them like a human being. The way you would if they were having a "physical" attack, because it's no different. You might think it is. You might a heart attack is an emergency because you think it can kill and mental illness cannot. And you'd be horribly mistaken.
I hope others have a better experience. I'd like to hear them, if you have. I'm sure the world is full of good and caring people who would stop and help a stranger in any kind of need. So please, if you've been in such a situation, please share if so inclined. It can, of course, be anonymous, as always.