Could be a prostate problem. I would guess that it also has to do with muscle tension. For example, in the morning when ya wake up theres a ton of piss in your bladder, but it's not a real urgent feeling, cause all your muscles are very relaxed, which is why you can wake up, hit snooze knowing that you have to take a major leak, but it doesn't keep you up. As the day goes on, muscle tension increases throughout the body.