I'm scared of melting down in public.

I travel next week, and for me meltdowns are a serious concern. When I reach a point of sensory overload there’s nothing left in me to hold myself together. I become non-verbal, what is called “selective mutism,” and I can’t talk if spoken to. Someone may say something like “Are you ok? Is something wrong? Can I help in some way?” but I’ve got nothing. I blankly stare, possibly shaking and crying. They dare not touch me, or things might not end well. The last thing I want is to be touched by someone when I’m having a sensory-overload experience.
 
With my partner, this is a non-issue, as he has been trained (by me) to know precisely how to help me safely navigate during challenging times like this. However, if I’m out in public, alone, a meltdown is the most terrifying experience I can imagine.
 
The last time I was in an airport I almost had a complete meltdown. It was mitigated by my catching myself in time and sitting on the ground, up against a wall, reminding myself to breathe deeply. I was able to get a friend on the phone who helped walk me through grounding myself, before it turned into a nightmare. Generally, I have a few moments/seconds before a full meltdown takes place. If I can’t regain control during this grace period, once the switch gets flipped and I go into a full meltdown- there is nothing I can do to come back until it runs its course. It can take anywhere from 30 minutes to a few hours once this occurs.