Mary's doctor would probably say to her that she has nothing to worry about. What her baby is experiencing is REM or Rapid Eye Movement. This is a stage of sleeping where a person has a low muscle tone throughout the body and a frantic movement of the eyes beneath the eyelids. In this stage is where we experience dreams more vividly and if we wake up we feel refreshed and alert. mary has nothing to worry about, babies tend to dream vividly even at such an early stage in our lives.
Hope this helps!