Having a romantic moment of intimacy is one of the highlights of a relationship. However, some people are worried that they won't be able to do as well as they think they should when it comes to lovemaking. The desire to please one's partner is normal, but when it starts to cause a problem, then it is labeled as performance anxiety.
There's nothing wrong with being somewhat anxious, but it becomes an issue when it has negative consequences such as low self-esteem, conflict in the relationship, avoiding sex and other sexual dysfunction. Any of these things are a sign that you should seek treatment for the problem.
It wouldn't be so bad if it happened only once, but anxiety doesn't work like that. Instead, what typically happens is someone feels they didn't perform as well as they could have, but they don't say anything about it. They internalize it and keep thinking about it…then the next time they have sex the performance anxiety is a little bit worse than it was before. It keeps getting worse and worse, until the moment of intimacy is a source of dread as opposed to a source of enjoyment.
One of the other problems is that the anxiety response can make sexual performance more difficult. When the body perceives a threat–real or imagined–it goes into fight-or-flight mode. You may feel sweaty, have a stronger heartbeat, and your heart will send blood to the your more vital areas first. Unfortunately, that means the sexual organs do not get all of the blood flow they may need. In other words, performance anxiety can actually cause more physiological problems, which leads to more anxiety, and it keeps spiraling downward.
Right now it may all sound somewhat bleak, but the good news is that there are things you can do to get your performance anxiety under control. The easiest thing to say is "don't worry about it", but that isn't realistic. The truth is that anxiety is a real problem, and it can't be ignored away.
It won't be easy, but you will need to talk to your partner about how you are feeling. Look at it this way: if the two of you are close enough to be having sex, then you are close enough to have an adult conversation about it. There are two of you in the relationship, so see what your partner can do to take some of the pressure off of you.
You may also be able to take some comfort in the fact that it's just your body's natural response, and not a sign that you are a weak lover. That being said, there are treatment options available to you, ranging from medication to coping strategies. You can use these separately or together. Everybody is different, so what works for them may not work for you, and vice-versa, but rest assured that there is something out there that will minimize or eliminate your performance anxiety.