It is of concern only to those around. There are no physiological indicators that the night terror is about to happen. The vast majority of nightmares are frightening REM dreams. Quite a lot of people suffer from them. Surveys indicate that perhaps a million people in Britain experience nightmares at a frequency of two or more a week.
Physiological measures start to increase perhaps several minutes before waking.
Heart rate and breathing rate climb steadily until the sufferer wakes in a state of great anxiety. Not surprisingly, some nightmare sufferers develop a distinct fear of going to sleep because of the certainty of waking in such an unpleasant state. It has not really been possible to deal with nightmares medically, but now a simple self-help method is available. Now that is guaranteed to bring on the nightmare. As was mentioned earlier, any thought in a dream brings about supporting imagery.