Managing mental and emotional states during competition, Allan, is a very complex topic. Certainly, I don't have the answer, only potential answers. But rest assured you're not the only player to ever "get tight" in matches. Most of us become nervous when we compete, in part because, quite simply, there's something at stake, something to be won or lost. And for whatever reason—take your pick: ego, biology, identity, social norms—winning is important. Hence the jitters, especially on big points. Missing a makeable forehand in practice is a nuisance, a mistake to be remedied; during critical junctures of a match, missing equates to a choke.
That said, what you're describing sounds not so much like a case of intermittent nerves as a form of background anxiety, an agitated state of being on court. This isn't good, not for your performance, not for your well-being.
So what to do? First and foremost, try to understand the origins of the anxiety. Are high expectations, perhaps, interfering with your play? How confident are you in your abilities? Take some time to think through these questions and ask others. In this respect, keeping a daily journal to record your thoughts and experiences can help, as can writing out positive narratives about how'd you like to respond emotionally in match situations. (For more on this, see "Tools for Mental Focus," a short piece detailing the value of personal narratives on performance.)
It might also be a good idea to begin working with a certified sports psychologist. (To learn more about how to find one in your area, click here.) But if that's not presently an option, pick up a copy of Dr. Steven Ungerleider's Mental Training for Peak Performance. Drawing on interviews with a number of world-class athletes and psychologists, Dr. Ungerleider, a practicing sports psych. himself, charts out a series of mental conditioning exercises designed to mitigate a range of impediments to high performance, including debilitating nerves.
The book is rich and multifaceted; I won't commit the sin of pretending to summarize it all here. Still, let me share with you one of the text's more interesting training suggestions: Mental Rehearsal. According to Ungerleider, when watching and playing sports, our minds are constantly capturing and storing sport-specific imagery. (In the author's definition, "imagery" encompasses not just seeing, but smelling, tasting, touching, and feeling as well; it refers to a full-on subjective reality.) In brief, Ungerleider writes,
"These pictures get called upon over and over—much as we call up information on the hard drives of our personal computers—and act as blueprints for our future performances. Imagery is based on memory, and we constantly reinforce the internal process by a flood of new pictures from external experiences to our minds. [But we] must also realize that in the process of expanding our repertoire—our imagery database—we can also create new images in our minds by practicing diligently."
Which, Allan, is your cue. Somehow, your "emotional blueprint" has been conditioned to react apprehensively during competition. Naturally, you need to retool this response, and one way to do that is to get into the habit of imagining—everyday, for 30 minutes to an hour—match scenarios where you play with not tension but relaxed confidence. This is called guided imagery practice, a form of which Ungerleider refers to as "Rewind and Review." As he instructs:
"Select a sport and begin mentally practicing it...Now imagine in your mind's eye your breathing and any amount of tension that might exist in your arms and legs. Notice if you are excited or aroused as you picture your sport. Next start playing and search your memory bank for a competitor or a teammate. Now imagine yourself executing a series of skills with your teammate or against an opponent. Notice your mistakes. Slow down the picture when you see a mistake, running through each frame in slow motion. Now speed up again to regular pace and continue to play well. If you see or feel yourself making a mistake in your imagery, slow down the visualization, correct the mistake, return to excellent play and speed up the mental tape."
Practicing this exercise on its own is a good start. But to get the most out of your time, there are other details that, Ungerleider believes, should be considered. For one, employing relaxation techniques before practice can make your imaginings more malleable and vivid, as can experimenting with various mental perspectives. Indeed, some athletes find it more helpful to see themselves playing in the third person, like a spectator, while others prefer a real-world, first-person view.
Regardless of which perspective you find yourself relying on most—ideally, both—the biggest challenge will be veraciously conjuring up the negative emotions you feel during competition, both in between and during points, and then consistently turning them positive. Try hard to make your mental rehearsal sessions appear and feel as real as possible; only then will what you rehearse translate into actual competition. As the saying goes, practice makes perfect, but only if you practice perfectly.
Be patient. Take your time. Tennis is, without a doubt, largely a mind game; the good news is, the mind can be reshaped, reformed.
