Let me explain. My son has a small typical night light that occasionally will go out, even if the bulb isn't dead. Usually I'll tap on it repetitively or shake it to get it to work again. When I hold it under another light, I can see the "coils" or string-looking things moving around uncontrollably, unattached to the points. Now, here's the weird thing. Sometimes, when I get it to work again, it will actually appear brighter than before. Usually it's an orangey-yellow dim light, but after it goes out and I "fix" it, it becomes whiter and brighter. How can this be? Is it because the coils are no longer connected in their usual triangular shape, instead forming an irregular shape? How could that effect it?
The coil is a resistor lets say its divided into three parts, they all have equal resistance (same material). If the coil in the bulb comes loose, it can short out at a different point. You have less resistance and more current through the same section of coil. This will make it brighter and also hotter and reduce the lifetime of the coil.
I've seen that before. You have a burned out incandescent bulb. The tungsten coil filament has disconnected from one end, but is being held onto the other reasonably well, and is acting like a spring. If it's jostled, the coil will sometimes strike its terminal and reconnect for a time.
When it does, there's no telling what part of the filament will connect, and as laptop2D describes, that's either cutting out part of the element (making it brighter) or paralleling elements that were meant to be in series (likewise).
I doubt it can overload like this for very long. Perhaps it's not overloading, and the effect you see is just a trick of perception.