It means you're most likely dehydrated and when u have to poop it restricts available real estate for little ones housing unit.

I got that once when I had to drink 5 cups of water before a ultrasound, I couldn't take it so I used the bathroom, thankfully I wasn't told to drink any extra water 

I've had that a few times but mostly it's cramping on my lower abdomen and I go pee and it mostly goes away. But I don't  have the I have to pee feeling it's like a full bladder cramp