If you are searching for this, something happened in your body and you are trying to find out what it was. So here is the practical distinction before anything else. Anxiety has a slope. It climbs over hours or days, it usually has an object even if the object is vague, and it tends to sit at a level where you can still drive, still work, still hold a conversation while feeling awful underneath.
A panic attack has no slope. It is close to vertical. The onset is sudden, the peak comes fast, and the physical symptoms are severe: heart pounding, chest tight, breath that will not go deep enough, sweating, shaking, hands and face going numb or prickling, waves of heat and then cold. Underneath all of it runs a certainty that something catastrophic is occurring right now.
The other feature that separates them is the trigger, or the absence of one. Anxiety can usually be traced back to something — the appointment, the money, the conversation you have to have. Panic attacks frequently arrive uncued. People have them in the grocery store, on the couch, waking out of sleep. There is no external reason, which is precisely why so many people conclude they must be having a medical emergency.
And there is the timing, which is the single most useful thing to know while one is happening. A panic attack is not built to last. The alarm response that produces it burns hot and burns out. The peak generally passes in twenty to thirty minutes, even when nothing is done to stop it. It will come down. It always comes down.