Have you ever found that right at the beginning of what is promising to be some good shut eye you are startled awake for no apparent reason? This is not unusual. Sleep has five stages. During the first stage, which is very light sleep, you can be easily awakened.
First Phase of Sleep
In the first phase of sleep, people sometimes experience the sensation of starting to fall and hypnic myoclonia, which is an abrupt muscle contraction. Consequently, you may jump and awaken. This is comparable to being startled while awake and jumping in response.
When you are startled, especially while sleeping, you will experience the fight or flight response, which makes you breathe faster and your heart beat more quickly. You have this reaction for a reason: to prepare you either to fight or flee. Your body’s response is to increase the rate of blood that is pumped to both your brain and your muscles. Your lungs take in big gulps of oxygen, and your pupils enlarge so that you can see better. When this happens, both your urinary and digestive systems slow down, so that you can concentrate. Of course, when you are startled awake at night, it generally isn’t due to a prowler in your room or a wild animal trying to attack you, but your brain and body don’t know that and automatically go into survival mode.
You may also be startled awake when you realize you are dreaming, that is, when you experience a lucid dream. Lucid dreams tend to be intense and realistic.
If you are startled awake during stage four sleep, which is deep sleep, you will feel disoriented and groggy. Becoming fully awake will take a few minutes, perhaps more.