I'm up late researching this, as my husband does this as well.  He is 34 (and a Capricorn  :)  Sometimes it's one leg, sometimes it's both.  I usually use my foot to slide his legs back down.  But he also lifts his arms into the air - sometimes just holding them there, but usually he puts his hand on his forehead, elbow in the air.  Sometimes it's just arms, or legs, or both.  I worry that this disturbes his sleep, as he does have a sleep disorder - but I don't think it's related to this behavior.  It's more disturbing for me, as when his arms fall, they often fall on me.  I don't recall him doing this years ago though, and am wondering if it could be stress-related?  Has anyone noticed if this behavior occurs when you are stressed?