This isn't directed at anyone here, I've just been hitting my head against a wall of willful ignorance and lateral ableism elsewhere and it's frustrating as hell.
Nonverbal isn't even the preferred term as it's a misnomer and it denies the fact that most non-speaking individuals have words, it's just about not having the ability to speak those words.
The clinical term for a person who cannot speak temporarily due to circumstances like being overstimulated or due to being anxious is selective mutism. You might hate the term and you're well within your rights to. I don't like it at all personally and I think that verbal shutdown is a better term. But that's a battle for the people like me, who experience verbal shutdowns, to wage in mainstream discourse.
What isn't okay is colonising the term "nonverbal" as this causes major problems for the non-speaking community because it promotes the false notion that nonverbal people can speak but they just aren't able to in particular moments. This makes accessibility much harder and it makes advocating for accommodations far harder as people in the community without disability will develop a fundamentally incorrect understanding of the needs of non-speaking individuals.
As an analogy, imagine if the accommodations for wheelchair users was based purely around the needs of people who aren't permanent wheelchair users and so the expectation becomes that things like toilet stalls, steps, and small amounts of walking are manageable for all wheelchair users without any adaptations or alternatives so therefore all of the accommodations of wheelchair users are only suitable for people who use wheelchairs part-time and who are capable of some amount of walking at any given moment - this would be extremely harmful to accessibility and to the wheelchair using community. In a similar sense, a person who experiences selective mutism and refers to it as "going nonverbal" can directly impact accessibility and accommodations negatively as it advances the concept that a non-speaking person just needs a little bit of time or a less overwhelming environment to speak rather than requiring the use of sign language or AAC.
The higher needs autistic community has been trying very hard to get people to understand why it's important to avoid the use of the term nonverbal/non-speaking except where it's accurate to do so but, unfortunately, the higher needs autistic community gets routinely overlooked and ignored.
I've just been trying to tell some people that they are misusing the term nonverbal, gently but firmly at first, and instead of taking this as a cue to do the basic research or to listen to leaders in the disability advocacy community who talk about being non-speaking and all of the issues around it, instead they are just digging their heels in and refusing to listen or even to just go and spend two minutes on the Wikipedia entry for selective mutism because they feel like their honour is at stake and that they must defend their claim over the use of the term nonverbal against all who threaten it.
Online discourse often frustrates the hell out of me. I'm polite and respectful unless someone is being intentionally disrespectful so it's not like I'm just yelling "You're wrong and stupid and evil!!" at a random person online but some people just refuse accountability and self-crit, and I lose patience with this because no amount of explaining the fact, quoting relevant information, or describing the negative consequences for others due to these actions is sufficient because some people's top priority is their ego and they just want to be free from genuine, good-faith constructive feedback.
Anyway, rant over.
Just try to keep in mind that the terms nonverbal and nonspeaking are intentionally specific out of necessity and try to remember to use a term like selective mutism or verbal shutdown when you're describing the intermittent phenomenon of losing your ability to articulate your words. It would mean a lot to me if you do and I know it means even more to the non-speaking community – this is one small way to act in solidarity with the disability community.
This is a good question and it's kinda beyond my paygrade so I'm going to do my best to answer it, but keep in mind that this isn't a definitive answer but just my best attempt.
So first off is that selective mutism gives the impression that it's purely a volitional thing where the person selects to be mute. This isn't the case though.
It's also worth noting that selective mutism can be more present than it is absent, so some people might experience selective mutism outside of their homes or whenever they are in a social setting where there is more than one person who can hear them, for example.
The distinction between being non-speaking (nonverbal) and experiencing selective mutism is that the latter has the ability to speak whereas a non-speaking person lacks this ability.
It might be useful for you to understand your own experience that you've describe as being on a situational low-speaking spectrum where, depending on the circumstances, your speech is limited by varying degrees and that this fluctuates.
If you are out engaging with people who don't know you and you are using alternative communication instead of speaking, I really don't think anyone is going to blame you if you use the label of non-speaking out of convenience because it's unrealistic to expect you to give every stranger you encounter a crash course in the difference between being non-speaking and selective mutism, and that's presuming that the other people are even going to have the time and inclination to learn about this in the first place. Sometimes you have to make compromises and accept the fact that we live in a society with a high degree of ableism and no one person is going to be able to resist the tide by themselves 100% of the time. Kudos to anyone who manages to do this but I think it's unfair to expect that every person with disability to become a tireless disability advocate - some people just want to live their lives and plently already face more than enough challenges without the need to take on the responsibility for reeducating of society at large and it's important to respect that.
So where does this leave you?
I think it's something for you to work through yourself so you can find a label or description that best suits what you experience. If you need to use a term like nonverbal out of necessity then so be it, but it might be worth shifting your choice of words towards something that allows for the distinction between experiencing significant challenges with speaking and those who are physically incapable of speaking.
I expect that this will take some time and that's okay. Unfortunately we all exist in a world where the level of disability awareness is really low and being disabled doesn't magically turn you into an instant expert in all of the terminology and concepts relating to disability, so allow yourself the permission to learn and grow at your own pace. It might be worth engaging with what's out there from non-speaking disability advocates and maybe even reaching out to them to have a discussion so that you can shape your own understanding and arrive at a position that you feel is aligned to what is both right for you and right for the broader communities of people who experience selective mutism and of people who are non-speaking.
Thanks for the response! That was insightful. I think what you said about being on a situational low speaking spectrum is really helpful. Since that feels fitting for me? I like it. It does feel worth shifting my choice of words for that distinction since, I'm not physically incapable of speaking. I can speak and say things, yet like, not exactly? It just feels more like I have a filter on my speech that just garbles everything and it just really makes it difficult and , and because of that, I'm just really use to communicating other ways besides speaking because of it. But I can speak just with difficulties, and so saying im non speaking just doesn't feel right. It def. would be worth for me to like reach out or at least read materials from advocates at the very least. Since in a way I just feel like im in a sort of odd spot? but seeing it as a situational low speaking spectrum helps a lot and I can also see how selective mutism applies to as well.
I'm glad that my reply is useful to you.
I remember the early days of when I started self-identifying as autistic, back before I got a diagnosis, and I learned about selective mutism and I was like "Well that's not me. I don't choose to go mute and I can talk just fine. Except for when I'm really overwhelmed or anxious and I often just say a few words even though I have a lot more that I want to say. And sometimes I give one-word answers or even just 'mm-hmm's when really I want to say a lot more than that. Hey, wait a minute..."
(Well, that's the condensed version of it at least.)
It took for me to conceptualise it as a spectrum and moving it away from a binary of mute/non-mute before it made more sense to me. In my experience I can almost always push through and muster at least a word or two if I really put effort in so the label of mutism didn't resonate with me at all. But I understand exactly what you mean by saying that it feels like a filter on your speech and how it garbles things because that's how it feels for me too.
I can definitely relate to that feeling of being in an odd spot. I think the more that this experience gets discussed amongst peers who also experience it, the better we'll be able to understand it and to communicate how it feels and what works when it comes to accomodating and supporting us.
Definitionally moving away from that binary of that mute/non-mute is very useful. It makes a lot more sense to see it that way. It just something I never thought as a spectrum before. And definitely talking about these things help a lot. I'm very isolated so seeing what you wrote or other discussions about similar stuff on here has been helpful, especially in also understanding myself as well.