Awesome tale and great advice! I bet you experienced a few moments that were, err, unconfortable …
Something similar happened to me a few years back. I was playing with a ridiculously over-powered “racer” MR I had built, 6000 watts of power. Tested static and in the yard, all good. Go to airfield to test some more and get some good speed, all good at first until at some point I switch to loiter, next thing I know it shoots up like a rocket at an incredible speed and becomes a dot barely visible then completely out of sight. All within what appeared to be an instant and before I had time to say “what the …”.
I freaked out and switched to stabilize and got it to slowly descend until I could see it, then land. In my case it was a typical case of excessive vibration, accelerometers aliasing and reporting no upward acceleration when it was climbing up, so controller kept asking for more upward speed. Later log analysis showed it went up vertically at close to 60mph!
Stabilize mode is our friend, one tends to never forget these sorts of episodes!