TLDR cardio saved my life recently

I started running at the beginning of COVID because I couldn’t lift at the gym. Three months into it I took my dog to a lake and was throwing a stick for him that (I now know) was too big. He got stuck about 1/3 across the lake swimming circles because it counter balanced him both ways. He’s too dumb to let go and I was about to watch my dog drown and do nothing so I swam out with my cloth and shoes on. About halfway to him I had to backfloat and just take my shirt and shoes off. By the time I got to him he was about 2/3 across and starting to panic. I rip the stick from him, try to at least but I’m absolutely exhausted. He gets a new grip on the stick and starts trying to pull back to the other side which I am definitely not going to make and probably not him. So I back float for the fifth or sixth time for a couple seconds while half drowning and him struggling a bit against me and with completely clarity realized if I panicked I was dead and THANK GOD I started running everyday a few months prior. I also remember my breath tasting like metal. I give one last yank and get the stick free from him and in front of me where I can kick push it to the shore. I finally make it with him following and immediately puke and fall asleep right there feet still in the water for a couple minutes. Wake up and I shit myself and the dog is staring at me just shaking and it wasn’t cold out.