"Hast nightmare" is a phrase that denotes a very unpleasant or terrifying dream, often causing the dreamer to wake up suddenly in a panicked state. There are many synonyms that can be used to describe the same experience, such as "terrible dream," "frightening vision," "horrific nightmare," "terrifying illusion," "dreadful reverie," and "nightmarish experience." These words can help to convey the intense emotions and fear that a person may feel during or after having a hast nightmare. Regardless of the words used, the experience can be disturbing and frightening, making it more important to seek out methods to reduce the frequency of such dreams.