Sleep, Interrupted

As far as I know, this is a common symptom of diabetes. I'm surprised your doctor wouldn't have at least mentioned that.

Not sure what sort of time frame you consider "before bed", but a fellow I know says he's stopped drinking water after about 7:30 PM to avoid nightpees. You might at least try.

Urgency is the desire to pee, regardless of how full the bladder is. It's not certain what causes urgency but some research suggests that it's pooling of a little urine in the bladder neck. A little urine might trickle in the connecting part of the urethra, sending off a signal to your brain that you need to go. Often, people have this problem after prostate surgery or other incontinence-corrective surgery. But I assume you would have mentioned that if you had it. I would guess (IANAD (IA 6 weeks into medical school) but I have done research on internal sphincters and incontinence) that something is amiss with the distal end of your bladder and/or your internal urethral sphincter. If the former is at a weird angle, then lying down for an hour might let a small (but present) amount of urine pool, causing the feeling of urge. If the problem is with the sphincter, then it might be letting a little trickle of urine in and causing the urge to pee. You mention that "25% of the time... [you] are unable to go". By "go" do you mean a voluminous torrent that would be indicative of the urge you felt or does literally nothing come out? Also, does lying down during the day cause this too or is only while sleeping? Either way, I would suggest seeing a urologist... maybe stick a scope up your urethra and make sure it's all good.

http://www.mayoclinic.com/health/prostatitis/DS00341/DSECTION=2?

You just wake up that one time--no other times during the night? The fact that you don't actually pee pretty much rules out diabetes or drinking too much. I'm pretty sure phantom needing-to-urinate feelings can be a sign of prostate problems, but I don't think they'd manifest just at one point during the day. You'd feel it all day and night long as the tumor (or whatever) pressed against your bladder. I like shokod's idea, especially since it only happens after you've been in an unnatural (wrt daytime) position for a while. Or, similarly, maybe you've got an internal organ rattling around in there (?!) and it settles onto your bladder when you lie down. In fact, my wife has noticed that having the cat sit on her hip while she's lying down makes her feel like she needs to pee. You don't have a cat sitting on your groin, do you? The theater comment makes it sound psychological, but that might be a red herring since a lot of people have this issue. ObIANAD

I would get the prostate checked out just in case--it may not be inflammed but hypertrophied that's causing the urgency, plus accounting for not letting you be able to start the stream when you want

This can be any of a variety of things. Your best bet would probably be to ask you doctor about trying an anticholinergic medication such as Oxytrol or Detrol, which are used for overactive bladder (that's what this sounds like the most). If that doesn't work, your next bet might be urodynamics, although the fact that your symptoms only occur at night might make whatever disorder you have difficult to reproduce.

By the way, the technical term for this symptom is "nocturia."

http://kidney.niddk.nih.gov/kudiseases/pubs/prostateenlargement/, benign prostatic hyperplasia, is very common. That's what this sounds like. Ask your doc about BPH. You're a little young for it but it is common. You'll get a PSA test to rule out prostate cancer (quite unlikely in someone as young as you are, so don't freak). If it is BPH it is easily treatable with drugs (Flomax is one, Cardura is another) that shrink the prostate. Basically the problem of BPH is a prostate gland that gets oversized and makes it hard to empty the bladder completely, and nocturia is a common first sign.