Playing your A game

There's plenty of winning players, who play until they are off their a game, and they become losing players. (mysellf included sometimes). They may make enough when they are on their game to make up for the times they are off, but if they overstay their welcome, and play too long, they will likely become losing players and lose everything they won and then some.
It can be frustrating. The main concept to avoid this, is to learn how long your game generally is "on" before it starts to slide. It should be at A game early, then it will slide to B, then it crashes and you go tilt mode. Then you might recover breifly and start winning, but then like someone who's nodding off to sleep and jolting his head awake real quickly before falling back asleep, your game will likely fall as well.
It doesn't matter what you do, but to avoid this, you must stop playing. go read a poker book, or go to a local card room, or go play live somewhere, or better yet, do something to completely take your mind off poker. Sure, this might be 20 minutes away from your playing time, but it will provide an hour of very solid playing time that is much more profitable...
Not only will you manage your bankroll better this way, but you will generally earn a lot more as well.
If possible, take a week vacation from poker every month or two.
In the long run, some might say, it's better that you deal with playing while not on your A game, and it's better to just switch down in limits. You will elarn to understand when your game is off, and you can just tighten up. By playing through your subpar game, you will learn to be a good player, even when you can't focus. This will allow you to develop a mental edge to the game.
While this may be true, there is no evidence to support it, and it is not worth the potential costs based on some theory. If you do want to improve your mental edge, simply gradually expand your time. So maybe you play an hour optimally. Go an hour and 10 minutes to really stretch yourself As you start to get comfortable go for an hour and 20 minutes, and then 125.
When sitting in front of a computer screen, it's hard not to get kind of zoned out, and to start playing mechancical, and exploitable, meanwhile being unaware of how long you've been playing or what time it is. So to avoid this, set a timer to make sure you do not overplay.
I have noticed I tend to do pretty well in cashgames, but an hour into it, I am pretty much done for, and I donk off a lot of cash to the point where I'm probably not even a profitable cash game player. With multitable tournaments I can last more like 2 hours, and my game doesn't usually get too rough, becausee I error on the side of loose aggression, which sometimes can be a good thing, but if I'm playing in the same tournament for 2 hours straight, my natural tendency is to not want to get knocked out, so in some sense, more loose aggression and making big moves can be good. It can also knock me out, but it will put me in position to make a big move a lot of times, which will result in a big cash. And even when making moves, it's not like cash games where I don't stop to think that my opponent showed a lot of strength, I just see 99 and a lot in the potand I decide to move in preflop.
In tournaments, I still know to make the moves that are profitable,l but have huge risks to them. A resteal all in, or a stop and go, or even a raise and go... I'm going to have to make a move at some point, so it usually won't hurt to make it a little bit earlier, against an opponent who isn't quite perfect for it as much. Plus with tournaments, you're going to see a lot of varience, and losing your buy in trying to make a move to get in the top money is never really a bad thing.
However, there is sometimes a big lost edge when I have a lot in chips and I continue to be aggressive late in a tournament when I already have tons of chips and there's mayb 2 tables left and I get involved in a big hand that I should just fold. Or at the final table, I'm 2nd in chips and I make a bad call when I could fold my way to 2nd, and instead I'm fighting for 8th.
So if possible, take a nap get sleep, get something to eat, go out, and make sure when you come back, you're on your A-game.
Always schedule breaks. Little things like these will allow you to save money when other players would lose it, and allow you to come back and make money when others would keep playing through their poor mental state, and continue to lose it.