My car shakes violently when I brake at high speeds

Yes, you should get this checked out soon but it's likely not an emergency. What you're describing is almost certainly warped brake rotors. When rotors get too hot (from hard braking, riding the brakes, or just wear), they can warp slightly. At low speeds you don't notice it, but at highway speeds the vibration becomes very obvious.

The good news is this is a pretty common and affordable fix. A mechanic will either resurface the rotors (if they're still thick enough) or replace them. Usually you'd replace both front rotors and the brake pads at the same time. Expect to pay somewhere between $300-$600 total at a regular shop.

Don't ignore it though. Warped rotors cause uneven brake pad wear, which means your brakes become less effective over time. In the meantime, try to brake more gently and avoid sudden hard stops. Also check your brake fluid level — low brake fluid can sometimes cause similar symptoms.

If the shaking only happens in one direction (steering pulls to one side), that could also indicate a stuck caliper, which is a different issue but still needs attention.