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.
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.