Ideally you know the dollar amount of your risk before you enter a position. I learned the concept of “Trading an R” from these guys > Real Life Trading
The idea is you define where you want to enter a trade and where you want to exit if the trades moves against you (your STOP LOSS). No matter what, you follow your plan. This always generates an odd number of shares/contracts based on the risk calculation, like 1,782 shares. Using the strategy, you know exactly how much $$ you will lose if you are wrong.
My fellow traders and I compare our “score” each month for healthy competition — even though we trade different $$ for our Risk Unit and have different account sizes, it’s a common denominator.
As far as dealing with the stress, I recommend you take a little time off - figure out what you would do differently & then do something fun, go out with friends and get your mind right for next week.