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.
Slowest Practical Shutter Speed for Handheld? I have never heard of the film speed rule but I have heard of the lens focal lengh rule. I use the focal lengh rule alot but I have had good results at 1/8 and 1/15 of a second. I do mostly portaits so I use a tripod 70% of the time.