You have to train in hardship to develop the ability to function in those conditions. You have to seek to increase your physical and psychological thresholds, and that's going to involve pain to both if done properly. We know the only way to grow stronger is to push the body to its limits, and this is equally true for martial practice. You need to train until what would once defeat you seems easy. The trick is you have to train until failure. No shame exists in such an effort; it is, in fact, growth. Change your mind to see it as such. Learn to see sparring/drilling/training to failure the same as you do in the gym. It means you had a good workout, right? That you will grow? This is also true of combat study.
You aren't just training, you are forging a stronger person. One who doesn't just survive, but can thrive in the heat of combat.