Sorry to hear about your pcs.
The second concussion usually has worse and longer lasting symptoms (depending on the severity).
The way I like to think about it is that my brain is kind of suspended in my head, but once you stretch the springs suspending your brain, they never work as well. If you hit your head again, the springs have less spring to continually protect you.

Basically once you have had one bad concussion don't fall or hit your head again...the springs are too stretched to protect you and the consequences will only worsen.

Good Luck on your journey!
Margarite