Hmmmm....okay, I'm finally motivated to contribute my thoughts based off of my research and practices on this topic.
Sleep Paralysis is a necessity that our bodies use when we sleep, obviously. The reason being is due to the fact that when our brains have activity (dreaming) that involves movement, generally the body will want to respond. Sleep Paralysis is used as a failsafe so that we don't act out (physically) any movement that may occur in a dream, which can cause self-injury. Though, there are cases when Sleep Paralysis doesn't take affect, hence sleepwalking.
Lucid Dreams, I truly see as a gift. Basically when you're Lucid Dreaming, you're in a Body Asleep/Mind Awake (Focus 10 trance) state. The things that can be achieved in this state are astronomical and can allow you to see and understand things better, which I'll explain in further detail.
For the past couple years now, I have been practicing meditation and have been researching and practicing OBEs (Out of Body Experience) and Astral Projection. In order to have an OBE or to Astrally Project, you need to be in a state where you are asleep but are conscious, hence the Mind Awake/Body Asleep. There are different stages of OBEs including RTZ OBE (Real-Time Zone) which your astral self is in the actual real-time environment. If you've ever heard of anyone talking about the Silver Cord, this is thought to be a link between your astral self and your physical self. I have seen the Silver Cord along with seeing myself asleep in my bed. There are also cases of people laying down a card face-up (without looking at it) in another room, having a OBE and looking at the card to find out what it is and then confirm it after they awake. Astral Projection on the other hand isn't in the RTZ; you are on the Astral Plane which is a whole different story. Although people tend to consider OBEs and Astral Projection the same thing, they are completely different; one is in our real-time environment while the other is on another plane. You have an OBE or Astrally Project every night when you're asleep but the memories are overwritten (just like with dreams) so you tend not to remember them. Even if you're conscious, sometimes it takes additional training to make sure you remember everything you've experienced in these states.
Sleep Paralysis and Lucid Dreaming both are extremely useful when attempting to have a OBE or Astrally Project because the work is done (your body is already asleep), you simply need to stay conscious and use the rest to your advantage to have a successful OBE/Projection. This is similar but not the same as NDEs (Near-Death Experiences) but a NDE is a form of a OBE.
Now, you may think I'm crazy but there are literally millions out there who are just as crazy as myself. Based off of what I have experienced first-hand and have confirmed by research, I am a strong believer on life after death and reincarnation. I wouldn't call myself religious (I don't believe in organized religion) but I am most definitely spiritual. These types of occurrences are actually being studied scientifically and I have even found information about how the U.S. government has a yearly budget to research this. Can you imagine what kind of espionage could be done with this ability?
Lastly, have you ever had a time where you have awaken to a jolt or jumped up out of bed? Everyone has had this happen to them at least once that they can remember. It is said that you wake up like this because your astral self realigns with your physical self too fast. Basically, when you're in astral form and you think of your physical self, you'll go back to it and sometimes it can happen a little too quickly. It is also said that when you have a "falling" dream, this is the cause of the falling sensation. When you land into yourself, you jump or jolt due to falling into yourself too quickly. I have also experienced this consciously, when I had my first conscious OBE.
Maybe this is a little off track but really, they're all in the same topic.