Can autistic adults have meltdowns or is that specific to kids? If they do, what does it look/feel like?
I'd like to start by talking about a couple of things as far as kids go. Namely tantrums vs meltdowns and how they're different. Also, this answer won't be immensely detailed scientifically or clinically and will more be explained from my perspective which I hope is okay 💜
Defining the difference between a tantrum and a meltdown is important I think in understanding meltdowns in adults. As they're often still viewed as tantrums.
As far as kids are concerned, a tantrum is a reaction to not getting something they want. It's a way for them oftentimes to cause a scene, because if they do so, the idea is that they'll cause enough trouble to get something they want. That's often how tantrums are in my experience at least.
A tantrum is a choice made by a kid to have an extreme reaction to not receiving something they'd like to have or they want to have something go their way. Often a child doesn't know how to react to not getting what they want. And so they react in an extreme way.
A meltdown is different in the fact that it is usually in response to something in the environment changing in a way that the brain has extreme difficulty processing. Perhaps it's a sensory issue, perhaps it's a sudden change in routine, a social situation that can't be handled, maybe many things at once.
This results in a meltdown for some. It's like an intense reaction to not being able to handle something anymore, to process it properly, and the bodies reaction can be very intense in that situation, its a complete sensory overload of some kind that the body or mind or both can't process and an intense reaction occurs in response to the high level of distress you're going through.
Tantrums are often a temperament issue in my experience essentially, whereas a meltdown is a processing issue.
Now, meltdowns can look like many things for many people. And I couldn't possibly explain them all. So I'll describe how it feels and looks like for me, and how I might react during one.
For me a meltdown starts as a pressure in my head. A feeling that won't go away. Sometimes I know the trigger and oftentimes I have no idea. But there's usually something happening or overwhelming me and this pressure that builds, it's distressing, I can't get it to go away, I can't make it stop, and it keeps building up because the bad sensory stimulation won't go away either, or my brain can't handle even after it stopped, eventually I start to lash out.
I often end up hitting my head because I want to tear out the feeling or I'll hit my bed or lash around and close my eyes really tight in an attempt to almost fling the feeling out of my body. Sometimes I cry and can't stop myself, sometimes it even feels like more than pressure in my head, it feels like my brain is burning somehow, just on fire in a weird way.
Sometimes it's a lot more subtle. Sometimes instead of lashing out, I maintain control over the feeling just enough to lash out at myself rather than the environment at all. But lash out still none the less. Or I'm able to somehow be on the verge of a meltdown but still manage to calm down.
Some people during a meltdown become self injurious like myself, some people become aggressive to others trying to help, oftentimes if that's the case I find it's because the other person is in some way adding more sensory stimulation in a way that isn't helpful to the person and so it's an attempt to prevent more of the stimulation.
I'm lucky and rarely have full meltdowns myself and more often just have a difficult time processing something where I'll just do one of the things on the list below or sometimes I'm able to just let it pass and be okay.
All that said, I haven't had too much experience with others having meltdowns except very infrequently but some things I notice about my own and some others I've seen or that I can think of that might help describe what it "looks like" would be the following
Cupping hands over ears to block out noise
Closing eyes tightly in an effort to escape light
Shaking or flailing body to try and "throw" a feeling out of the body.
Intensely stimming in an effort to replace a certain stimulation with a more pleasant one in hopes of calming myself down
Humming loudly to try and hear that noise rather than another
Squeezing my hands as tight as I possibly can
Hitting any part of my body like my chest or legs repeatedly
Rocking back and forth, usually with eyes squeezed shut and hands over ears
Isolating in a dark space or corner
I hope that was helpful and explains decently enough 💜 thanks for the question.