Stress and fear of the unknown can trigger some interesting human behaviors, including the need for incessant nervous chatter. There are some people who cover their feelings by filling the air with words, a condition sometimes called logorrhea. Many cases of true logorrhea are connected with diagnosed manic conditions, however, not the chattiness of a first-time flyer or nervous public speaker. For most people, talking serves as some sort of calming mechanism in reaction to certain stressors.
Not everyone talks too much when they become nervous. Some people tend to shut down verbally when faced with a stressful situation. The last thing they want to do is appear too talkative or sociable. But a number of people find talking to be a stress reliever, at least for themselves. As long as they can continue talking, other thoughts and fears cannot enter their consciousness. A nervous flier, for example, may talk his way through the entire take-off process as a way to reassure himself nothing is going wrong.
Other people talk excessively when nervous as a way to establish a bond with others, albeit an imperfect one at times. A nervous job applicant may spend her time talking to other applicants in order to calm down before an interview. By expressing her fears and making small talk, she may be able to gain enough confidence to handle the interview better. One person's talking can often encourage others to share their own experiences or concerns.
Another reason some people talk too much when nervous is a temporary loss of focus. This happens quite often when a speaker forgets a crucial part of a prepared speech and is forced to improvise. The fear of leaving out some critical fact or observation can cause some people to go into verbal overdrive. Some speakers may feel nervous due to perceived time constraints, so they will speak much faster than normal. Once a person has had time to collect himself or herself, however, the need for excessive talk often dissipates quickly.