Learning to recognize when you are mentally compromised is an essential aspect in trading.
Unlike trading robots, we do get tired after a certain time and the chart patterns all start to look like happy (or sad) faces and the lines all start to blur. It is also around this time that tunnel vision sets in and you start to loose track of why and how you got into this trade to begin with.
As I took note of my trading, I noticed that when I started my trading day, the first few trades are usually well executed, clear and concise and I ended up making pips. Even if I did not make money, I still traded my plan and felt good that I did not deviate from it. I have also found that I personally can be fully attentive for about 3 to 4 hours. After that, things can and have gone south very quickly and I return all the money I made a few hours ago.
All this to say is - be vigilant. Being mentally compromised is when you feel agitated, confused, doubtful and frustrated. You close positions early and take small pips or let run loosing positions and take large losses. All these are some of the symptoms of being compromised.
The best way to keep a clear tab on this is by having a trading journal and a section where you enter your "mood", "Clear and ready to trade", "tired and frustrated", etc. By doing so, you can also clearly see a time during your trading day when you start to go mentally south. So put in big bold letters "Mentally Compromised!" in your journal. Seeing it over and over again will allow you to recognize when it starts to happen and pre-empt it by shutting your computer off.
Hope this has helped you identify and improve your trading. Good luck!