What causes extreme fatigue, chronic bilateral arm and leg weakness with sudden onset, difficulty getting up from a sitting position and imbalance, tremors and jerking in left leg and hand, and stuttering. all of which can go away as fast as it comes?

You need to see a neurologist for an evaluation, including a physical exam and diagnostic testing, to find out what the problem is so that it can be treated. This sounds like a neurologic issue so a neurologist is the best doctor to see to begin the process of diagnosing the issue. ANy medications you take also need to be reviewed for potential side effects. Good luck!