One hypothesis says that this happens because you are starting to dream but you are not fully asleep and this is a symptoms of both of these things fighting.

Another evolutionary hypothesis claims that this happens because this was the body’s way to wake up our ancestors before they fell out of the trees.

Namely, when your brain is confused, it will restart and you will wake up with a burst of chemicals. This is however not dangerous for your health, but it is still not a very good feeling. There are still also those opinions that twitches are connected to early onsets of Parkinson’s disease or Alzheimer’s, brain injury or nerve damage. But this is if it is too serious.