As it turns out, I recently had an experience that I considered sharing, then changed my mind, then saw this post.
I had my gear serviced (as we all should) and after the service re-routed hoses, replaced my "necklace" and did everything necessary to make sure I was confident in my configuration. I mean I spent a couple of hours going over everything to make sure I knew that everything was tight and ready to dive without issues.
The next day my dive buddy and I made what we would consider to be a fairly conservative dive but still technical. My newly serviced reg (Poseidon Jetstream) was breathing just fine. Actually was impressed with the way it was tuned. We explored one area, then turned to change direction and explore another. As I was swimming, I turned my head to look to the right, then I turned and looked to the left. Suddenly I had an explosion of bubbles in my face and inhaled water. The water hit the back of my throat, but I exhaled it through the reg (I thought) before it got any further. The next breath brought nothing but water which didn't get very far before I exhaled it again, but this time I spit out the mouthpiece and grabbed my backup underneath my chin.
My backup reg was delivering air, seemed to be without any issues, but I COULD NOT GET ENOUGH AIR. By now my buddy had come to assist me and had shutdown my reg that was freeflowing (Thanks buddy!) . I should mention that we were diving in an area where you can only see what your light shines on (There is no light in there...and yes we are both fully certified) I motioned to him that I was having trouble breathing and wanted to share air (I DID NOT GRAB HIS FROM HIM), and waited until he was prepared and handed me his reg. I continued to try to breath from his reg with the same result as breathing from my own (couldn't get enough air). He gave me the "OK" I answered with "problem, hard to breath" and "thumb up" to end the dive. We made our way to open water and began our ascent still needing to deco. When I got to about 50 feet, I was still breathing uncontrollably and finally just closed my eyes. Stop, think, breath. I got it under control. Gave buddy his reg back, and went back onto my backup. Picked up my deco bottle and completed decompression all the while thinking about what had just happened. Found my primary reg and discovered that my mouthpiece was missing. Then, all of a sudden, it was clear to me what had happened (I honestly did not know up until that point).
1. I never checked or tightened the zip-tie on my mouthpiece (checked everything else twice or three times, but not this 2 cent piece of life support equipment)
2. A mouthpiece without a regulator is a straw when you are underwater.
3. When you inhale to start the flow of gas and then lose the mouthpiece on a jetstream, it freeflows like mad.
4. When you are in a place where there is no light, an explosion of bubbles (strong enough to unseal my mask) in the face while you are gagging on water is not immediately identifiable as something that has a good reason (from now on it will be).
5. When water hits the back of the throat, even though you might be in control of everything else, you cannot control (without thinking about it) your body's desire to breath hard and fast.
6. Closing the eyes and focusing on breathing (nothing else matters until this is under control) works, but you have to first...close your eyes....second....breath calmly and deeply until it is under control. Stop, think, breath (from OW training).
I have intentionally left out dive profile information, location, etc. because I wanted to tell the story from the perspective of my feeling. It was terrifying and I do not scare easily. I was as close to panic as I think a person can get without being completely out of control. A lost mouthpiece on a reg is probably not a big deal if it is a sunny day, plenty of viz and it does not happen in the middle of pulling a breath. But, what if viz is bad? What if it is a night dive? What if you aspirate the water? What if my buddy had been same day same ocean (I would have shutdown my own post, but you get my point) instead of hovering a few feet away from me.
I learned a few valuable lessons, and I hope my experience at least gives you something to think about. I took something for granted (that my zip-tie was tight) even though I checked everything else and could have drowned as a result of it. I'm not saying that you can't trust LDS, just that you should check your own gear fully. Putting a mouthpiece back on a regulator for a customer, can't possibly be done with as much love as doing it for yourself.