What is that feeling?

Robert124 said:

Meltdown, shutdown, panic attack.  I admit that I don't know the difference.  But I used to suffer from something similar for many years.

My problem was trying to walk into pubs, clubs, canteens (school, college and work).  People are talking, eating, drinking.  And when I try to walk in my legs freeze and feel actual pain, my head gets this weird feeling like my brain contracts to a tiny point inside my head, sometimes chest tightness and pain and I can't move forward, when I try to force my self forward I start to get a blackout and lose consciousness.  When I retreat backward the symptoms ease.  I don't know what the medical term for this is.

What you have described here are anxiety or panic induced shut-downs when losing consciousness, or lock-ins when freezing, with the freeze reflex being another aspect involved with the fight or flight reflexes that ordinarily get triggered in order to survive life threatening scenarios, so in your case it seems as such that you were experiencing lock-ins and shut-downs as a result of a 'Social Anxiety Disorder'.

Meltdown, shutdown, panic attack.  I admit that I don't know the difference.  But I used to suffer from something similar for many years.

My problem was trying to walk into pubs, clubs, canteens (school, college and work).  People are talking, eating, drinking.  And when I try to walk in my legs freeze and feel actual pain, my head gets this weird feeling like my brain contracts to a tiny point inside my head, sometimes chest tightness and pain and I can't move forward, when I try to force my self forward I start to get a blackout and lose consciousness.  When I retreat backward the symptoms ease.  I don't know what the medical term for this is.

Later people accuse me of being anti social, a snob, thinking that I'm too good to sit with them etc.

I think if you can switch it on and off, it's probably anxiety/sensory overload not a full-on panic attack, because you can't usually control a panic attack. Anyway I'm glad that earplugs are making your life easier!

The NHS has a page about panic attacks if you want to check. www.nhs.uk/.../.

The one time I had a 'big' panic attack it very obvious what was happening. My heart suddenly starting beating really hard, really fast, like it would when I am sprinting, I had a cold sweat and I dissociated (I felt like I was floating outside my body).

I think a meltdown is more of an emotional response rather than physiological, e.g. getting very overwhelmed/uspet about something and crying loads. I would usually get over it quite fast when I leave the situation.

Sometimes I am not sure if I've had a 'panic attack' or if I have just been feeling panicked. However, does it really matter? The same techniques will help for preventing it.

Meltdown and panic attacks are related. But this sounds more like a shutdown. Shutdown is kind of the same phenomena as meltdown, but exhibits in the opposite directionn; freeze rather than fight.

All these responses come up from the amagdala in response to sensory overload which is causing anxiety. Hence why you feel better with the plugs in. Panic, would see you hyperventilating.

Thats great, and yeah, exactly the effect noise cancelling has had on my bodily response to it. Wish I'd known long ago

I’ve always had a sense of irritation/uncertainty in busier/noisier places, and always just put it down to a sense of general grumpiness! 

I had my verbal ASD diagnosis 2 weeks ago, and over the weekend I went to a museum exhibition. It had only just opened and was pretty busy. I felt that usual feeling creeping in, but in light of my diagnosis I did something I hadn’t done before. I put my earphones in, turned on the noise cancelling, and found a white noise track to put on loop. 

I was amazed at what a difference it made. Previously I probably would have just left, annoyed and let it ruin my day. But this time I almost gave myself permission to deal with it differently, and it really seemed to work. 

A meltdown usually describes an experience/event were you seem to have lost all control and cannot seem o get things under control again. This often refer to children but sometimes adults who then scream, or pull at hair, or flap hands, or bang heads on walls, or so many physically expressions seen.  This usually requires intervention to help get back under control.  
Anxiety are reactions to some event that are often quieter- a tense feeling -a sense of confusion at what is happening, and often the person knows they are anxious and their need to handle it somehow.  When you are older, you act nervous/anxious and develop a plan- ex. Crowds make you anxious so you avoid crowds and/or make plans to handle it in the future. Often when Autistic people are anxious/ facing the freeze/ things are illogical an adult can leave the scene- breathe, and process the event.     I hope this helps. Either way- this is here seeing a professional counselor could help.

I don't really get meltdowns, but my understanding is that "meltdown" isn't really a technical term, it's just a colloquial term for an extreme panic attack caused by emotional or sensory overload. Certainly the few I've had have been like that. But I'm prepared to be corrected on this!

Outer noise leads to inner noise, I find. Ear defenders *really* help me.