Most likely it is an adrenaline rush, but for your peace of mind, you should just go get a physical and maybe an EKG. If everything is okay with that and you know you are okay, the next time it happens you will be able to handle it.
Anxiety causes a lot of adrenaline rushes for me. It could even be a subconscious thought that I am not aware of (example - seeing a commercial for a dentist on television and that could trigger a subconscious dentist fear that brings on the rush).
Do get checked out just to be sure. Also, discuss with your doctors any medications you are on and what side effects they may be causing.
Good luck and let us know how it goes!
Lindaru