If you lay down for half an hour and stand up and it happens again id check with your doc. With my daughter my sac was leaking from the top i noticed it when i got up one morning i thought it was urine as well but then it happened every time i got up out of bed went in and they almost sent me home because i was not having contractions but they did a test and it was fluid chances are it could be extra fluid or discharge but better safe than sorry
In any event when u don't know best is to call ur doc.
Not sure what urs is but I had something similar happen with my first. It was a sudden gush of fluid. No smell and clear. I went to the doc they said it was just extra fluid.
If it was amniotic fluid, it would continue to leak.
Actually, it might not be urin at all. More commonly it could be discharge. Happens to me all the time... if it was fluid.. it wouldnt stop at all. With my son, i thought i peed myself of my water broke... nope it was just a heavy flow of discharge.. same with my daughter and same with this one now.
Put a pad on. If you soak it within 1 hour, it is fluid. If its not leaking continually, it was most likely urine.