Chess may actually be a less visual thing that you might think.
Good chess players tend to "feel" the position and how something might be captured rather than visually check and spot it. Of course they will visually check for stuff as well, but still a lot of that depends on their feeling. Like how a lot of people claim not to visualize the board at all when they play blindfold chess, they simply "know", an inner logic or memory of where the pieces are and where they can go to.
Here is an example in my last game, with my post-game analysis.
Again, I had a zap at 10... b5 ??, leaving my Knight behind completely undefended.
This is the kind of chess blindness I talk about, even when I'm fully concentrated. It's discouraging. 
Notwithstanding also that I acknowledge in my analysis that I missed the tactical opportunity with the pinned Knight, the Rook exchange at the end that would have placed me with a dominant mating threat. I was getting close to a time crunch and missed that the pin gave me a tactical opportunity.
usually it happens because you haven't "seen" the pattern enough times. In the example you posted, I've made that type of mistake myself many times before, even recently. It just hasn't happened enough that I can condition myself to look for that all the time.
usually it happens because you haven't "seen" the pattern enough times. In the example you posted, I've made that type of mistake myself many times before, even recently. It just hasn't happened enough that I can condition myself to look for that all the time.
Also a funny thing is that better players are vastly more likely to get away with that kind of thing, because nobody ever expects a top player to leave their knight hanging even in a blitz game, you just wouldn't even consider it and the response from the other top player is sometimes as if it was defended exactly like in this game here.
I used to have this problem a lot, but I got past it (mostly lol) through pure experience. I have played almost 2,000 games now on chess.com, and I guess I just have more of a "feel" for the position than I did when I was 800 rated or so. OP said they have been playing chess since they were a kid, so this advice might not apply, but I would say to just play more games and you will develop that intuition to stop making blunders.
Here is an example in my last game, with my post-game analysis.
Again, I had a zap at 10... b5 ??, leaving my Knight behind completely undefended.
This is the kind of chess blindness I talk about, even when I'm fully concentrated. It's discouraging.
It's a matter of training yourself to think of two separate things, before moving.
1) Before making any move, try to figure out what your opponent's best response (or best responses) may be. So if you're going to attack your opponent's queen ... don't just stop there. Try to figure out where your opponent's queen may move, after that.
Don't just try to find your own best moves - try to find your opponent's best moves, too. Sometimes, this can lead to you seeing an idea that you might have missed, otherwise. "Let's see, if I move here ... where can he go next? here, or maybe here ... or ... OH! Wow, he can do THIS ... That would not be good. Hmm.. Maybe I shouldn't move there, then ..."
2) Pawns can't move backward. So whenever considering a pawn move, first ask yourself what that pawn is currently doing. What square does it occupy? What squares does it control? Once you move it, these answers will change.
In the above scenario, you should have made a mental note that your pawn is currently supporting your knight on a6. By noting that, you would have then realized that moving that pawn would suddenly make the knight vulnerable.
Just two simple things to train yourself to think about, before making your moves. They won't solve all your blunders, but they might help decrease their frequency, just a bit. 
I used to have this problem a lot, but I got past it (mostly lol) through pure experience. I have played almost 2,000 games now on chess.com, and I guess I just have more of a "feel" for the position than I did when I was 800 rated or so. OP said they have been playing chess since they were a kid, so this advice might not apply, but I would say to just play more games and you will develop that intuition to stop making blunders.
Just to add more info, I used to play scholastic tournaments until I was around 12, then stopped playing tournaments in my teens, because I did not see any real progress and other aggrieving factors in my personal life made it harder for me to find a motivation.
I became more of hangaround at the chess club during high school, playing a few games here and there from time to time. The chess mentor there did take time to teach me some concepts and encouraged me to stick around, and was connected enough that a number of Masters and IMs would be passing by from time to time when there were international tournaments in the big city. However, the blunders still remained and adult life forced me to move, so I stopped playing completely around college.
My last game went smoother.
Won on time, and did made some mistakes and missed some tactics... but the main plus was that this time I did see obvious blunders before playing them, and even a counter-mate.
I am quite satisfied with this one; looks I am seeing some improvements. 
What?
Well, I haven't succeeded yet. If I have a lot of time on my hands, I can play calmly and usually avoid these kinds of mistakes, but if I'm under pressure my tunnel vision increases, I forget where the pieces are, and ... there goes my queen.
I'm trying to improve this through discipline: taking the time to consciously assess the situation with each move. Yes, as you said, it requires a lot of mental energy. Eventually I would like it to become an unconscious awareness of what is happening on the whole chessboard, but I can't get to that point without first educating myself to build that habit.
One way I am trying to deal with this issue is to acquire a high-level view of the chessboard in terms of the threats and mobility of the pieces. For example, instead of remembering where some enemy pieces are, I try to remember which diagonals, rows, or squares would not be available for my next moves. It sounds like a small conceptual difference, but it made things a little easier for me.
I have begun to study some strategy, and I hope that training myself to evaluate a position will help with "chess blindness" as well.
Another unexpected "trick" I discovered is that using a smaller virtual chessboard leads to greater awareness of it. If I am on the desktop, I resize the board so that it is easier to get the full picture. On physical chessboards it might be different; I have yet to test it on my two chessboards, one of which is small and portable.
As for dealing with the more emotional aspects, this book contains some suggestions for avoiding mistakes such as the one described. It is not a book focused on avoiding mistakes, but it contains interesting suggestions on how to deal with the game from an emotional point of view.
Here is an example in my last game, with my post-game analysis.
Again, I had a zap at 10... b5 ??, leaving my Knight behind completely undefended.
This is the kind of chess blindness I talk about, even when I'm fully concentrated. It's discouraging.
Notwithstanding also that I acknowledge in my analysis that I missed the tactical opportunity with the pinned Knight, the Rook exchange at the end that would have placed me with a dominant mating threat. I was getting close to a time crunch and missed that the pin gave me a tactical opportunity.
Don't be too hard on yourself. You must have assumed that the knight on a6 remained defended after b7-b5 since it was previously protected by the knight.
We are human. It's normal to make these types of mistakes. Our ability to make such errors dissipates over time as we gain experience.
Because yes, I am chess-blind.
It's my personal #1 stumbling block. Always have been, from my kid years to being an adult. Still, in my own recent games, it's a recurrent factor in my games. I am not playing crazy and sacrificing pieces left and right... I am not talking about not being able to make calculations... I am talking about missing the simplest of material loss or obvious capture, which immediately loses the game. 1-0; 0-1.
I also believe this is the case also for most amateur or learning players as well; not just beginners who barely know how to move the pieces, but even more intermediate and advanced players who have their theory straight, but just fumble the ball every single game. It's called "making blunders", but it's more complicated than that.
I feel quite a few IMs and GMs mentors doesn't "get" that - for a good number of players, for various reasons, the brain just zaps somewhere random and they miss the obvious undefended piece, or the Queen being attacked.
Now, I am not anxious about losing games. I have been losing some and winning a few all my life. Wins and losses will happen and, well-fought, they are opportunities to learn and improve.
I am not even anxious about making mistakes. A game without mistakes is a draw. My job is to make the fewest possible but mistakes happen, and they are why we have winners and losers in a chess game.
BUT chess-blind blunders... these are what drive me anxious to the point my stomach churn while I play. The fear of slipping almost makes me paranoid and self-conscious. One may study chess theory for hours, do chess tactics to improve both tactical vision and instinct, acquire the building blocks to play a great, solid game... and for 30 moves, it works. Until BAM! On the 31th move, you go "blind"... a miss the obvious and you lose; game over, and you remain stagnant.
In other words, the fact of the matter is that I may fetch all the best, most expensive pieces to build this magnificent Ferrari in my garage, my car will remain 100% worthless if its engine stalls everytime at a random stop. So I need to work on that engine... but it still occurs.
That is what blocks me from improving... and this truth will hurt... it's the player's fault.
It's my fault. I am 100% responsible for my own mental vision. I am not putting this into words to put the blame on something else, I just describe how it happens when it does happen - even if deep down a lot of it is a matter of self-discipline.
The only way for I found to try to build that discipline is through mental crutches to stop myself from missing stuff, every single turn, hoping I don't slip until, I hope, it becomes someday second nature - checking for checks, captures, and threats every single move I play, or keeping my eyes laser-focused on the chessboard. This takes enormous brain power, though just to maintain that continuity in focus at all times so I don't forget which pieces are where. And again, it might just slip on a random turn, either because I become tunnel-focused, hyped, or part of the chessboard disappear from view and mind, I stop doing it.
That, and play slower. I try to budget a portion of time every move, even if it looks so self-evident... but from bitter experience, sometimes it is when it is self-evident that the blunder is there. That is why I am weary from playing blitz - I just dont feel ready for it. It just magnifies one's blindness to play so fast.
So... how did you personally fight and win against chess blindness? How do you manage this wheel of fear and emotion? How did you manage to win and to 'no longer be blind'?