There is a process of getting a job where you and a complete stranger are shoved into the same room, neither by choice, and are forced to pretend to like each other for thirty minutes. If, by some miracle, you two actually get along, the person being interviewed might get hired. If not, you're quickly forgotten as the other person gets shoved into the same room with a completely different person. This process is not exactly technical nor scientific, and it sure as hell doesn't depend on you or your personality.
This is something you have to understand to function in an interview environment. It is not about you at all. Doing well at an interview consists of three primary skills. First, reading body language. Second, holding a conversation on just about goddamn anything. Third, using the first two skills to figure out what the needs of the interviewer are and meeting those goals, both spoken and unspoken.
As I noted, these skills have nothing to do with you. They have to do with your ability to watch the interviewer and respond to their needs. For example, you come in the room and the interviewer looks bored out of his skull. Quickly figure out how to grab his attention and keep it.
When you put things in this perspective you see why getting nervous is a waste of time. Getting nervous results from overthinking your own role in the situation and underthinking the interviewer's. Don't worry so much about yourself. Worry about them.