I play a fair amount and shoot anywhere from mid-80's to mid-90's. 77 is my best, which I've done twice and feel lucky to have done.
Reading this story, I can feel your pain. I think sometimes the internal pressure of saying "I need to make par-par for 76" or "double on 18 gets me in for a 79" is just too much for amateur golfers. Don't take that as a slight because it happens to me and any of us, really. But my 'recommendation' (though based on this story, I think you should be telling most of us how to play golf) is to not put that pressure on yourself. However you were feeling on the front 9, where you blistered that side in 4 under and pushed to 6 under after 10 - recapture it. You weren't going from hole to hole with the negative thoughts of what could happen but rather playing your game and letting the chips fall where they may. For amateur golfers, rather a single digit handicap or a guys who shoots >100, this is the mentality to have. Not trying to be too preachy or cliché but I truly believe this is the attitude you need to have when you play.
Even in my best rounds, I have never shot 4-under on one side or even for a stretch of holes in the middle of a round. That's phenomenal golf. Sometimes, if you feel like you can't play any better than you did it's best to just pick it up and feel like you conquered it for a day. In the end, the game always ends. Whenever I shoot close to even par on 9, I just say to myself, 'I should retire' haha.
Anyways, thanks for posting. It was entertaining. I hope you succeed in your pursuit for 70's the next time you tee it up!