That sounds like a panic attack, so the general advice works here too. Here’s some advice from people smarter than me.
At an actual demonstration I would suggest repeating the chant, and being prepared. Being prepared is having all the notes you need in case things go south and that you are connected to your group. And supplies like water and milk of magnesium in case of tear gas. No shame in wearing a helmet or any amount of protective gear you can tolerate, the police do.
Those nerves are a big part of the reason for the chants like “not another nickle, not another dime.” Shouting them with the chant leaders should help with those kinda nerves. Let your fear and nerves flow into it.
If you’re having a panic attack while watching videos, turn them off and take a break. Nothing good comes from watching too many of them.
Yeah that’s a good point, we should all probably wear helmets to any protest with a high potential for police brutality, concussions suck. All other body armor can be mostly concealed in clothing.