Nightmares are simply dreams that bring about feelings of anxiety, dread, or fear. They can affect anyone of any age regardless of gender or ethnic background. They can be short, repeating episodes or a long and complex sequence of events. In most cases, nightmares seem very real to the patient, even a few seconds after waking up. The actual causes of nightmares can be difficult to determine, and they tend to be different for different people. Some people experience nightmares after taking certain foods, spices, or medications. Still others experience nightmares after going to sleep exhausted. For some patients, marijuana may be effective at reducing the severity and frequency of nightmares by bringing about a more relaxed state prior to falling asleep.