Dream is a semi-conscious state where we have absolutely no control over our thoughts and expressions (unless we master lucid dreaming). Did you know that most of us spend six years or more of our lifetime dreaming? Research proves that all of us dream at least twice or more in our sleep though we may not remember when we get up. In 5 minutes of waking, half of our dream is forgotten and within 10 minutes, almost all dreams are forgotten. People who are blind from birth too dream.
It is just that the dreams of these individuals are formed by other sense such as the touch, smell, sound and taste. During roman era some dreams were even discussed and interpreted in the senate as the dream was considered to be a God sent message for the mankind. Lucid dreams are considered those dreams where person can take full or partial control of their dreams. Most important fact in order to be aware that we are dreaming is practice.
Writing down and keeping track of your dreams is very important. Second thing is noticing signs or triggers that can help us stay aware that we are in dreaming state. Once we start dreaming lucidly we could control the imaginary experiences in the dream environment. This is extremely important for people that have nightmares. Interesting facts is that our body is paralyzed during our sleep probably to prevent the body from acting out dreams.