Why do your legs have a spasm when you fall in your dream?

Question: Why do your legs have a spasm when you fall in your dream?
- Keywords:
  dream,
  leg,
  spasm
Asked by rachieb97 to Damien, Rachael, Simon, Suzi, Tim on 17 Jun 2011. This question was also asked by okelly.
- Suzi Gage answered on 17 Jun 2011:
  
  Hi @rachieb97
  There have been a lot of questions about dreams, you can have a look at some of the other ones and their answers here:
  /brainj11-zone/search/dreams
  
  I don’t know the answer to your question, but I assume that similar to the crying question, when your brain is imagining falling, similar parts of the brain are firing to if you were actually falling, so your body can sometimes react. When you dream, you are in something called REM sleep, where your body is pretty much paralysed, probably to stop you from fully acting out your dreams – these twitches are all that get through that protective paralysis.
  
  Hope that answers your question a bit, it’s just my theory!
  What do you reckon?

Question: Why do your legs have a spasm when you fall in your dream?