Any painful event can start a cascade of response chemicals. It can also create a startle response or an anger like response that will cause this cascade of chemicals. Although you were not anxious about the event, your body has responded in a way that is similar to bumping your head.

The sternum can a very sensitive spot, even if just for a short period.

I know that I can experience a painful event that triggers me for at least a day. I might end up shaky and nauseous with what I call a mud headache.

Try to relax and treat your headache and you will get through this.

My best to you.