Got the same problem sleepwise. I'm OK during the day and normally but lying down just brings it on - I assume something iscausing pressure on the bladder.
Anyway I've had tests, including the camera up me, and nothing is obviously wrong, so I'm still at a loss until I visit my doctor. I did get some medication from the urologist which helped, but that was only temporary as I could not be on medication when taking tests.
Dunno if it's a man thing only but saw palmetto and zinc tablets from the health shop have helped a bit.