sleep running SJ

Every once in a while, SJ will sleep run.  I would say sleepwalk, but he appears to be running from something.  When it occurs, he seems very agitated.  We assume that he is having a nightmare.  He will run downstairs and try to open doors.  This concerns me, because I am not sure if he will accidentally leave the house.  Fortunately, my husband and I are usually still up when this happens.  My big worry is that we will be so exhausted from our day that we will not hear him.  So far, we have always heard him.  One of us will then steer him back to bed.  Last night, he had three episodes of this sleep running before he was able to remain in his bed.  I asked him this morning if he had a bad dream last night.  He gave me his typical response of "I don't know".  I wish I knew what was upsetting him, so that we could talk about it with the next day.  The good news is that even after three of these episodes he still is his happy self the next day.  Maybe one of these days he will outgrow this behavior.  Until then, I will sleep lightly!