Most all of us have had bad dreams and called them nightmares.
Nightmares are long, frightening dreams that often wake the sleeper.
They may involve long scenarios in which the sleeper is in some way rendered vulnerable or afraid of being hurt or chased. Although frightening, nightmares are not necessarily any cause for concern. They tend to be more frequent at times of change and stress. In addition, some medications may cause a chemical change that may bring out nightmares. In contrast, night terrors are episodes of panic which may cause a sleeper to bolt up suddenly, screaming in terror.