In OCS they aren't going to allow you to stick your butt up in the air, shake out your arms or any of that stuff. If they catch you they may or may not warn you and then they will tell you that you are done. As for sagging your body, well that would probably be a little easier to get away with, but if they catch you then you will be done there too. The folks at OCS go by the letter of the instruction strictly. You can rest in the up position only. And they will watch for the arms parallel to the ground, blah, blah, blah. Things in the fleet will be a little less stringent. Of course when there are 6 classes doing the PRT all at once at 0500 in the morning, some things will be missed. But I the extra time it will cost you in OCS if you don't pass it is definately not worth the chance.