The first stage is the NREM stage. This is the earliest phase of sleep when you are still alert and can be awakened easily. It may be termed as the transitional phase. You enter a stage of dizziness but are relatively alert to any external impacts. The brain starts producing alpha and theta waves in this stage. In this stage of sleep, you may experience vivid sensations and strange bodily experiences like falling from a long distance. These sensations are known as hypnagogic hallucinations.
Another experience, known as a myoclonic jerk, also occurs at this stage. This is when you feel startled suddenly during sleep or experience body jerks for no reason. Though it may seem uncommon, we experience this phenomenon more than we realize. The first stage of sleep lasts for approximately fifteen minutes, after which we move to stage 2 of sleep. If someone wakes up during the first stage of sleep, they may even feel like they were not asleep at all.