Actually, there is a more plausible reason for this reaction. It's called a muscle spasm.

The mind works in mysterious ways. I once learned in a psychology class that this is most likely caused by a relaxing muscle suddenly spasming, and the mind incorporates it into your dreams, turning it into falling off a step or tripping, for example. Of course, this is only theory, but it seems much more plausible than a "memory" of millions of years ago.

Mi"liked that class a lot"a