Facial twitch: I believe these twitches are similar to the twitches people get in their eyelids. Usually it goes away within 6 weeks or so. There are other causes such as caffeine, stress, alcohol, electrolyte imbalances and excessive fatigue. Feel better.
A shutter speed of 1/30 for example will let in twice as much light as a speed of 1/60 since it is two times slower. When you decrease the shutter speed by a factor of two you are increasing the amount of light by one stop. Remember that fractions get larger as the number on the bottom gets smaller.
The photo below was shot on film but, if i remember rightly, it was f/1.7 for 1/30 of a second at ISO 200. The point here is that, if you want to take a well exposed photo in low light, you need a lens with a wide enough aperture to let more light in. Setting your lens to stop at f/1.8 actually lets in 4 times more light than f/3.5, which is a huge difference for a small change in number.