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.
A larger max. aperture also allows you to use a faster shutter speed to freeze action. So, let's say the light meter in your digital camera calculates that for proper exposure in that indoor arena, you need an aperture of F4 and a shutter speed of 1/60 sec.