The stages of sleep make for some of the most eventful times of our entire day. I don't care how busy you are awake, when you're asleep, you're putting in double time.
The phase of first phase of sleep (alpha state) occurs as you are drifting off and when you first wake up are a lot like the feelings of hypnosis, body is afloat, mind is not engaged on analytical thinking, you simply exist. This is a key time for slipping in and out of the body in out of body experiences/astral projection and also visitation from the dead. If awakened in this phase, you may feel like you didn't sleep and your body might also jerk as if you are falling. This lasts perhaps 5-10 minutes.
The second phase of sleep, your muscles contract and relax repeatedly throughout, the heart rate slows, the temperature drops. The body at this point is preparing for deeper sleep, going into almost a hibernation physiology.
The third and fourth stages take you into the deeper realms. Three is deep, but fourth is intensely deep. The brain waves slow and if people are awakened at this time, they will be hard to arouse. We go in and out of REM (rapid eye movement/dream state) for short periods. This occurs about every 90 minutes. During the deepest stages, the body repairs and your immune system strengthens. As we age, we get less of this restorative sleep.
Thankfully, our bodies go into a paralysis during the deeper stages and so when we do have dream state, we don't act on them, though sometimes these functions are disrupted and hence there is talking and walking, even eating in one's sleep.
If someone tells you they had a weird night's sleep, well, that's more the norm than we realize. Unusual sleep events do happen because of the delicate balance between the sleep phases, environmental interruptions, chemical influences from medications, and exhaustion.
We also tend to change up the themes on our dreams during the night, to where we left off anxiety and fear, steam and anger in the earlier dreams and work into problem solving in subsequent dreams until morning when we might start having pleasant, happy, hopeful and arousing dreams.
Sleep walking and talking. When sleep paralysis phase is interrupted, the body can move, both mouth and legs. Some people get up and actually make food and eat while their mind is still in sleep state. There are some people whose transition from sleep states are more ineffective so that they are more prone to talking or walking in sleep. It has also been shown that certain drug effects can alter the sleep state, as in the case of people taking sleeping pills and even driving asleep.
Out-of-body experiences are described as a sense of leaving your body (like in near-death experiences) and traveling and witnessing things in other locations. I have had these to such a degree that I communicated with someone in another country, in her apartment and then the next day asked her if she saw me there. I described the apartment, how they were speaking, what her fiance looked like who was standing behind her. She was shocked. She had seen me in her apartment and worried that I wouldn't understand her speaking slowly to speak English clearly. I had wondered in the encounter why she was speaking so oddly. We might possibly have OBEs in our sleep more than we know. I have gone places and learned things in my sleep that I couldn't have known, details about people's homes, what they wear to bed, what's on their walls, the books on their shelves.... The only warning I have is a super high vibration in my entire body so that it feels like every cell is fluttering like a million hummingbirds. This occurs upon leaving and reentering.
Encounters with aliens and the dead.
You are most likely to have an alien encounter or a visitation from the dead in the sleep state between stages. Some people report sleep paralysis with this and associate that with the aliens controlling their body, but sleep paralysis with waking encounters are common. I have had them where I open my eyes, see the room, but cannot move my body. That's a part of sleep staging. It's what you seeing during that time that is questionable. If you are still in a dream state, it can appear that you seeing things not there, like the hallucinations of dreams. It's a catch-22 when understanding these encounters. Were they genuine encounters done at this time because the mind is in a state to perceive and not a threat or are they result of dream state interfering on waking state? I can say that two of my encounters with greys in my room, I was moving around, in fact, the first time, I swung my legs over to go to the restroom when I saw one in front of me, I also crawled across the bed to try to touch on. I could have been asleep, but all sense were involved in this encounter including sense of smell and temperature, light and I was up and studying the window's view within seconds.
I've had these for decades and they are unsettling. I did learn a commonality - it is a premonition dream if no one in the setting sees or hears me. I'm there as a kind of witness. I have gone down with many airplanes, been hijacked, survived earthquakes and tidal waves. I am not sure why these events can come through 24-48 hours beforehand, but they can and some of us have an uncanny ability to see a dream come true. If the pineal gland truly is the third eye and it is the regulator for our sleep and dream state, there might be a tie-in.
Paralysis is important in sleep to keep us from hurting ourselves, but sometimes it can be terrifying if you start becoming conscious during it. I've awakened during anesthesia a few times (redheaded complaint) and it is horrifying. In one case of sleep paralysis, I fell asleep on some cushions on the floor watching a movie. My eyes fluttered open and I saw the credits scrolling but I could not move my body. I felt strangely heavy and drugged. My mind felt foggy and weird and I interpreted this as the screen scrolling safe harbors to go to in my neighborhood during the ongoing nuclear attack. I wanted to read where to go, but my eyes weren't clear and I couldn't move and felt drunken. I thought perhaps the radiation had already affected me. It was horrifying.
This happens more often to children, but adults can get them too. It can happen when you are overly exhausted and go to bed or taking medications. A shift in the sleep and wake state makes you have a nightmare that you are able to scream, sit up, throw your arms about and fight off an imagined threat and can be very difficult to calm down.
As you can see, with so many possibilities in the dream state, we seem to have lots of chances for things to go wrong, but also chances for interactions our brains can't perceive in our analytic awake state.