It's pretty common with Hypervigilence running riot.
It also happens with SPD (sensory processing disorder) kids, as well as a few other disorders. Even if you don't have trauma related to crowds. Essentially, your brain is trying to process everything because of the hypervigilance and getting completely & totally overwhelmed. It's hard work.
Some things that help:
- Scanning... Deliberately look at an area before entering into it. Note features, note traffic patterns. Mark exits. Give your brain a moment to pay attention to everything, with nothing else competing for its attention.
- In crowded places... Sit in a corner, ideally, or back to a wall. That deletes 1/4-1/2 of the room your brain is trying to pay attention to / gives it a null space to rest in. Also saves on neck-aches & ear strain, since you're not constantly checking what's behind you. A nice quiet safe wall is behind you.
- Sugar... Forget fish, your brain runs on glucose, and glucose alone. All that work your brain is doing? Burns a lot of sugar. Converting glucose (the simplest sugar) from complex sugars (most carbs) is totally possible, but it takes effort. Having a bottle of soda or sweet tea, or a few sugar cubes or candies to suck on will greatly improve that muffled/ crosseyed/ fatigue/ headachy feeling... And lower the anxiety that spikes when that happens (and your brain starts hollering at the digestive system to convert-convert-convert-noooooooooow!!! like the wild haired PMS lady with a gun next to a Haagen-Däs truck.) Sucrose... That super processed only 1 step away from glucose that everyone says is bad for you... Is best. Unless you can get your hands on some diabetic glucose candies.
- Limit your options... *Music can be a great way to tone down how much work your brain is doing. I do have trauma directly related to crowds, so I can't do this, exactly. Serious anxiety spike if I can't hear everything going on around me. ONE earbud, however, will provide a normalizing backdrop for all the other sounds. It really, really helps me. For others? It can be just one more sound contending with every other sound. *Another trick is turning down the volume. Drummer's Earplugs, or Shooting ear plugs allow crystal clear sound to pass through (unlike regular earplugs which muffle sounds), at a lower volums... And eliminated the screeches & booms of upper and lower registers. By either drowning out, providing a unifying backdrop, or turning down the volume? It limits all the sensory information competing for your brain's attention.
- Grounding... Ah, grounding. Useful so many places!
- Timeouts... Bathrooms, parking lots, service hallways, rooftops. Wherever is quiet, peaceful, and away. Apply liberally.