How could a coffee mug slide off a level table by its own power?

How could a coffee mug slide off a level table by its own power? Serious question here... Full cup of hot coffee my wife brings me. It is on the night stand and a good 5-7" from the corner in both directions. The night stand is stable and level. There is no possible way it could fall off the table. As I'm watching TV, the coffee mug somehow slides across the table and hits the floor, top side down. I am not near the cup in any way I could not have hit it. The wife was with me, heard the slide and saw the drop. We looked at every possible scenario such a leaning table (all level). Cats were accounted for. Room is brightly lit. Nothing fell from the ceiling, and we went over, logically, every possible scenario. I am not superstitious. So I know there must be an answer for this. Now, the table was waxed with a heavier wax because it was getting water marks but that was many weeks ago. However, the wax often times caused thee coffee cup to stick (I used actual wax). When something warm sits on it without a coaster, it sticks on occasion. My 'theory' is that the warm cup initially stuck to the wax, the cup them became sealed. Could the heat have built up in the ceramic from the freshly heated coffee and caused the air pressure to build under the mug, causing it to jump off the table? Ideas welcome, I'm really perplexed over this! And quite frankly, got me a bit spooked. I've had a cup do something similar, not to the point of breakage, but something I noticed once. I think that it's related to the surface tension of water that might be on the bottom of the mug. You mentioned that you were getting 'rings' on the table and you've waxed the table. Just a theory here, but suppose the bottom of your cup is a concave area and you've got a little bit of water/coffee/whatever on the bottom of the cup. When you set it down, you've made this little sort of cushion of air get trapped under the cup by the surface tension of the water, effectively creating the situation you've described. Try it. Pour out a tiny bit of water on the top of your table. Set your cup down on it. Move it around a little bit, and you should see that it slides very easily.