leaking pad or not?

Your suspicion is correct, the pad is loosing volume do the the decreased pressure from the cooling air. Using an inflator rather than your lungs should mitigate that issue, since you would be filling it with air that is already air temperature, rather than 98 degrees.

It will also prevent a moisture build up, which can supposedly damage the pad over time.

Maybe, probably. There are three basic components to inflatables: Bladder, Valve, Air Pressure.

Bladder: A leak can develop in the bladder. If you get a puncture, of-course, it is usually catastrophic and will just flatten within a few minutes. A micro-puncture can develop through a poor coating. Often this will develop after a year to three years of heavy use. As Matthew was saying, saliva is nearly a universal solvent and can cause damage to a coating. You might have gotten a very small puncture from debris you might have missed. These types of small leaks often show up in a water bath as bubbles on the surface of the pad as opposed to a chain of bubbles. They can be difficult to detect in a water bath. Often with a poor coating, you may see an area of a few places that will form bubbles. Patching any leaks is SOP, but you may have to return/replace it if it is a poor coating. That will take 5-8 weeks.

Valve: The valve is exposed to all sorts of external debris. If any scratches or other debris interferes with the seal, you might find a slow leak there. Sometimes, tightening the valve can prevent leaking. A good firm twist can do it, AFTER blowing the valve out a bit. If this happens a lot, I would suspect a scratched or damaged seal. On occasion, your only choice is to replace the valve, I have a spare around here, I think you *can* get them from Therm-a-rest but I am not sure about replacement, I never had to do it.

Air Pressure: The most common is simply temperature changes. This may make a pad seem like it is leaking. As the pad cools off it will loose pressure as the air shrinks. This is unlikely the problem if you have to do this in the middle of the night, though. It *might* loose 10% between ~100F and 32F. If you start with a soft pad, it could mean it is air pressure leaving you touching the ground in the middle of the night. The other thing is Barometric changes. If you go to bed in a low pressure system (read rain storm,) it can soften somewhat in a high pressure system. But this will not likely happen consistently. The combination of the three, softer pad, temperature and air pressure, could result in having to add air in the middle of the night.

I use this technique when I get to camp. I unload my tarp (setting it up,) stove, cooking gear, food and pull out the Neo Air. I give it a few puffs of air (enough to unroll it and puff it up.) Then I put my sleeping bag, shaking it out for about 30 sec, and lay out my sleeping gear & set up my pillow. If I am soaked I may change cloths and cook under the tarp. Anyway, just as I turn in, I blow the pad up again. After about an hour in camp, the pad should be close to ambient temp, so don't over inflate it. Just firm it up. Often by morning it is slightly soft, but it held through the night, fine. It has been like that since I got it…no better, no worse. I believe it will always leak a bit and if I really worried about it, it would be annoying, but I ignore it and it works fine. I believe it is about 5-6 years old, now. I'm not sure because I replaced it soon after I got it due to "ballooning," it is one of the originals and there was a manufacturing problem. On occasion, I have left it at base camp and taken a day hike to another location, and it still is mostly inflated when I get back, two or three puffs of air will re-do it. It gets used 45-70 nights per year.

It really seems like it leaks slightly, but most "air containers" do. Car tires require monthly adjustments. Bike tires have to be done every week or so. Balloons go flat overnight. And so on. That the NeoAir also leaks a slight bit does not bother me…it is expected.