Penis doing weird things on it`s own (FYI...not another erection question)

So I have noticed that when I am laying on my back to sun, my penis will be laying towards the right then all of a sudden it will kind of point towards my chest and then go to the left.  I can see it sort of pulsing with my heart beat, but again it has nothing to do with an erection as I am not "excited" or "touched by the wind" etc.  My testicles also do this thing where they "churn" kind of move in circular motions towards my body and then back down??? I guess I have never really examined or stared at another guys penis so I am just curious if this is normal?
While at a nude beach this was happening and I rolled over even though it was not something I thought was not to be hidden, but wasn't sure of what others thought.  I also am average sized, but not hung so does the weight of a hung penis hold it in place so this doesn't happen?  When it moves and goes towards my chest I worry that people might think I am getting a semi-erection when I am truely not.
Any feedback would be great.  This will for sure not stop me from visiting nude beaches etc, but just wanted to know if it is something other guys experience?