There is more than enough good advice here that is hitting all around the mark and is very useful for reflection. But, without more information it is hard to really know where you are at.
Some have suggested that in fact it may be that the system is in a normal drawdown. It should be easy to find this out by comparing your actual trading results to the trading results called for by your method. If they diverge, then your problem likely is internal. If your results match your system's results, the likely you are feeling anxiety from a normal drawdown.
But it sounds like to me that indeed there is a discipline breakdown. If that is the case then rather than reacting to the breakdown, get better at understanding the clues or cues that lead up to the large losses. I know for me when I start pulling my stops (even when it works out), or not exiting when my profit objectives are met, or start taking (or even considering taking) trades that are not signaled by my system, then I start sensing that a discipline breakdown is in the works. Then I either center and refocus on my objective (following my system), go back to paper trading for a while, or I just shut it down for the day if I am too emotionally caught up in proving something or in being right. It is times like these when I switch over to system testing/creation as my head clearly isn't right for trading.
Ultimately I have found that discipline comes down to a basic decision. Every minute of every trading day we make this decision. It is true that poker can help put things in perspective. Meditation can do that as well. But the decision has to be made and adhered to tenaciously. Your choices are to either follow the system regardless of the outcome, or to prove something - be right - make something happen, etc.
If you choose to follow the system (method), then you are in the right frame of mind. But as soon as you start wanting to prove something, or to make something happen, or you are certain such and such will happen if you just hold on to this unprofitable position a little longer... as soon as one of these things takes over you are bound for a losing ego roller coaster ride.
Set a maximum daily loss and leave the house after that has been reached.
This a good suggestion but really to have the discipline to adhere to this you have to be in the right frame of mind - the one that is willing to follow your money management "system".
For me the turning point was just getting sick and tired of losing. I couldn't take it any more. I finally decided that I was willing to do whatever it took to stop losing even if it meant I would have to let go of my ego and follow my rules. Until you reach rock bottom and get so tired of losing, and become willing to do whatever it takes to overcome this problem, all the good advice in this thread will really not amount to anything. In the end it comes down to introspection and determining what you really want out of trading. Right now it might not be what you *think* you want. Your results are just an outward manifestation of your inner desires.
There is one other thing that I started doing that has helped me stay more emotionally level from day to day. Instead of mentally labeling winning days "good" and losing days "bad", I started labeling all trading days "good". Every day is now either a "good earning" day or a "good learning" day for me. This means I have a homework assignment on "good learning" days to see what lessons I can learn from what has transpired on this day.
I also got better at disassociating myself from my trade to trade and daily results, because they are less a function of me than a function of the positive expectancy of my system, and how well I followed my system, so it really is silly to feel either elated or upset when my system either makes money or is unprofitable since I am merely the one putting it in motion. My profit goals have moved from day to day to weekly goals - my goal is to be profitable every week. This takes a lot of the pressure off on unprofitable days when I realize that this is just one of many days this week. Even one unprofitable week now is just one week among many weeks.