I don't know how to swim and have almost drowned a few times (~8) from not really respecting that I can't swim effectively (actually from reading the top link from ColinWright I am tempted to do a "AskHN: Best way to learn how to swim as an adult?" there seems to be a lot of knowledge here on this subject)

One of those times was particularly bad and someone had to come in and rescue me. I had gone to a swimming pool the day before and done a couple of strokes and thought to myself "this isn't too bad" but then we went to this cliff next to a flooded canyon where people like to jump into the water (it's very deep but only around 10 meters across and you have to swim across to get to the cliff). I wanted to be safe so I started by going parallel to the bank to be sure I could do it but after doing a stroke and keeping my head out of water I thought "what the hell I'll go for it" and turned while swimming and started going across. With no experience and a very out of my element I was rushing and basically managed to exhaust myself when I was half way (I could have gotten to that same spot in one kick from the bank probably). It was a very strange feeling I couldn't move at all! My body was completely exhausted and I couldn't summon an ounce of energy so I started to drown. The issue was that no one really took it seriously and my friend who was standing on the other side and had said he'd help me if anything went wrong was just looking at me like "come on.." so gradually my panic rose and rose until my face communicated sufficient terror for him to realize that I was going to die.

The problem of course is when you are really panicked this climbing response (that I just learned about today by reading ColinWrights top link in this thread) kicks in and you become dangerous. I did know that panicking people tend to kill their would-be saviors in their panic but I wasn't really thinking..

Anyway he jumps in and I bear hug him instantly and we both start drowning, except I realize we're going to die and go completely limp just keeping my hand on his shoulder and my eyes open. He manages a stroke or two and then I do the climbing response and pull on his shoulder and manage to grab a rock and pull on it and boom I'm up and standing on the other side wheezing and coughing and with a crazy headache.

It's very important to start saving at first signs of trouble and not waiting for signals of distress, by then people have already lost their rationality. I think what saved me is just how mentally prepared I was for this exact scenario and also having experienced it before but with no one to help me (needing to breath out all air and walk on the bottom of the ocean / pool to find something to grab / float with). Being careful about not breathing in water (better to suffocate) and having done a bunch of yoga was also useful.

My biggest lesson was that swimming isn't binary, anyone can swim, it's more about the gradual efficiency improvements you make. Since then I've made some progress in learning to relax again and now I know how to float on my back but I'd like to buy a buoy for open water swimming and start practicing in the ocean. I'd love it if anyone can inform me of the sanity of that plan or give me good resources and advice.